如何将hello world程序写到极致

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#include<bits/stdc++.h>
#include <cassert>
#include <cctype>
#include <cerrno>
#include <cfloat>
#include <ciso646>
#include <climits>
#include <clocale>
#include <cmath>
#include <csetjmp>
#include <csignal>
#include <cstdarg>
#include <cstddef>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <cwchar>
#include <cwctype>
#include <ccomplex>
#include <cfenv>
#include <cinttypes>
#include <cstdalign>
#include <cstdbool>
#include <cstdint>
#include <ctgmath>
#include <cuchar>
#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <exception>
#include <fstream>
#include <functional>
#include <iomanip>
#include <ios>
#include <iosfwd>
#include <iostream>
#include <istream>
#include <iterator>
#include <limits>
#include <list>
#include <locale>
#include <map>
#include <memory>
#include <new>
#include <numeric>
#include <ostream>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <stdexcept>
#include <streambuf>
#include <string>
#include <typeinfo>
#include <utility>
#include <valarray>
#include <vector>
#include <array>
#include <atomic>
#include <chrono>
#include <codecvt>
#include <condition_variable>
#include <forward_list>
#include <future>
#include <initializer_list>
#include <mutex>
#include <random>
#include <ratio>
#include <regex>
#include <scoped_allocator>
#include <system_error>
#include <thread>
#include <tuple>
#include <typeindex>
#include <type_traits>
#include <unordered_map>
#include <unordered_set>
#include <shared_mutex>
#include <any>
#include <charconv>
// #include <execution>
#include <filesystem>
#include <optional>
#include <memory_resource>
#include <string_view>
#include <variant>
#include <latch>
#include <numbers>
#include <ranges>
#include <span>
#include <stop_token>
#include <semaphore>
#include <source_location>
#include <syncstream>
#include <version>
#include <barrier>
#include <bit>
#include <compare>
#include <concepts>
using namespace std;
// Components for manipulating sequences of characters -*- C++ -*-

// Copyright (C) 1997-2021 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library.  This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 3, or (at your option)
// any later version.

// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.

// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
// <http://www.gnu.org/licenses/>.

/** @file bits/basic_string.h
 *  This is an internal header file, included by other library headers.
 *  Do not attempt to use it directly. @headername{string}
 */

//
// ISO C++ 14882: 21 Strings library
//

#ifndef _BASIC_STRING_H
#define _BASIC_STRING_H 1

#pragma GCC system_header

#include <ext/atomicity.h>
#include <ext/alloc_traits.h>
#include <debug/debug.h>

#if __cplusplus >= 201103L
#include <initializer_list>
#endif

#if __cplusplus >= 201703L
# include <string_view>
#endif

namespace std _GLIBCXX_VISIBILITY(default)
{
	_GLIBCXX_BEGIN_NAMESPACE_VERSION
	
#ifdef __cpp_lib_is_constant_evaluated
// Support P1032R1 in C++20 (but not P0980R1 yet).
# define __cpp_lib_constexpr_string 201811L
#elif __cplusplus >= 201703L
// Support P0426R1 changes to char_traits in C++17.
# define __cpp_lib_constexpr_string 201611L
#elif __cplusplus > 201703L
#endif
	
#if _GLIBCXX_USE_CXX11_ABI
	_GLIBCXX_BEGIN_NAMESPACE_CXX11
	/**
	 *  @class basic_string basic_string.h <string>
	 *  @brief  Managing sequences of characters and character-like objects.
	 *
	 *  @ingroup strings
	 *  @ingroup sequences
	 *
	 *  @tparam _CharT  Type of character
	 *  @tparam _Traits  Traits for character type, defaults to
	 *                   char_traits<_CharT>.
	 *  @tparam _Alloc  Allocator type, defaults to allocator<_CharT>.
	 *
	 *  Meets the requirements of a <a href="tables.html#65">container</a>, a
	 *  <a href="tables.html#66">reversible container</a>, and a
	 *  <a href="tables.html#67">sequence</a>.  Of the
	 *  <a href="tables.html#68">optional sequence requirements</a>, only
	 *  @c push_back, @c at, and @c %array access are supported.
	 */
	template<typename _CharT, typename _Traits, typename _Alloc>
	class basic_string
	{
		typedef typename __gnu_cxx::__alloc_traits<_Alloc>::template
		rebind<_CharT>::other _Char_alloc_type;
		typedef __gnu_cxx::__alloc_traits<_Char_alloc_type> _Alloc_traits;
		
		// Types:
	public:
		typedef _Traits					traits_type;
		typedef typename _Traits::char_type		value_type;
		typedef _Char_alloc_type				allocator_type;
		typedef typename _Alloc_traits::size_type		size_type;
		typedef typename _Alloc_traits::difference_type	difference_type;
		typedef typename _Alloc_traits::reference		reference;
		typedef typename _Alloc_traits::const_reference	const_reference;
		typedef typename _Alloc_traits::pointer		pointer;
		typedef typename _Alloc_traits::const_pointer	const_pointer;
		typedef __gnu_cxx::__normal_iterator<pointer, basic_string>  iterator;
		typedef __gnu_cxx::__normal_iterator<const_pointer, basic_string>
		const_iterator;
		typedef std::reverse_iterator<const_iterator>	const_reverse_iterator;
		typedef std::reverse_iterator<iterator>		reverse_iterator;
		
		///  Value returned by various member functions when they fail.
		static const size_type	npos = static_cast<size_type>(-1);
		
	protected:
		// type used for positions in insert, erase etc.
#if __cplusplus < 201103L
		typedef iterator __const_iterator;
#else
		typedef const_iterator __const_iterator;
#endif
		
	private:
#if __cplusplus >= 201703L
		// A helper type for avoiding boiler-plate.
		typedef basic_string_view<_CharT, _Traits> __sv_type;
		
		template<typename _Tp, typename _Res>
		using _If_sv = enable_if_t<
		__and_<is_convertible<const _Tp&, __sv_type>,
		__not_<is_convertible<const _Tp*, const basic_string*>>,
		__not_<is_convertible<const _Tp&, const _CharT*>>>::value,
		_Res>;
		
		// Allows an implicit conversion to __sv_type.
		static __sv_type
		_S_to_string_view(__sv_type __svt) noexcept
		{ return __svt; }
		
		// Wraps a string_view by explicit conversion and thus
		// allows to add an internal constructor that does not
		// participate in overload resolution when a string_view
		// is provided.
		struct __sv_wrapper
		{
			explicit __sv_wrapper(__sv_type __sv) noexcept : _M_sv(__sv) { }
			__sv_type _M_sv;
		};
		
		/**
		 *  @brief  Only internally used: Construct string from a string view
		 *          wrapper.
		 *  @param  __svw  string view wrapper.
		 *  @param  __a  Allocator to use.
		 */
		explicit
		basic_string(__sv_wrapper __svw, const _Alloc& __a)
		: basic_string(__svw._M_sv.data(), __svw._M_sv.size(), __a) { }
#endif
		
		// Use empty-base optimization: http://www.cantrip.org/emptyopt.html
		struct _Alloc_hider : allocator_type // TODO check __is_final
		{
#if __cplusplus < 201103L
			_Alloc_hider(pointer __dat, const _Alloc& __a = _Alloc())
			: allocator_type(__a), _M_p(__dat) { }
#else
			_Alloc_hider(pointer __dat, const _Alloc& __a)
			: allocator_type(__a), _M_p(__dat) { }
			
			_Alloc_hider(pointer __dat, _Alloc&& __a = _Alloc())
			: allocator_type(std::move(__a)), _M_p(__dat) { }
#endif
			
			pointer _M_p; // The actual data.
		};
		
		_Alloc_hider	_M_dataplus;
		size_type		_M_string_length;
		
		enum { _S_local_capacity = 15 / sizeof(_CharT) };
		
		union
		{
			_CharT           _M_local_buf[_S_local_capacity + 1];
			size_type        _M_allocated_capacity;
		};
		
		void
		_M_data(pointer __p)
		{ _M_dataplus._M_p = __p; }
		
		void
		_M_length(size_type __length)
		{ _M_string_length = __length; }
		
		pointer
		_M_data() const
		{ return _M_dataplus._M_p; }
		
		pointer
		_M_local_data()
		{
#if __cplusplus >= 201103L
			return std::pointer_traits<pointer>::pointer_to(*_M_local_buf);
#else
			return pointer(_M_local_buf);
#endif
		}
		
		const_pointer
		_M_local_data() const
		{
#if __cplusplus >= 201103L
			return std::pointer_traits<const_pointer>::pointer_to(*_M_local_buf);
#else
			return const_pointer(_M_local_buf);
#endif
		}
		
		void
		_M_capacity(size_type __capacity)
		{ _M_allocated_capacity = __capacity; }
		
		void
		_M_set_length(size_type __n)
		{
			_M_length(__n);
			traits_type::assign(_M_data()[__n], _CharT());
		}
		
		bool
		_M_is_local() const
		{ return _M_data() == _M_local_data(); }
		
		// Create & Destroy
		pointer
		_M_create(size_type&, size_type);
		
		void
		_M_dispose()
		{
			if (!_M_is_local())
				_M_destroy(_M_allocated_capacity);
		}
		
		void
		_M_destroy(size_type __size) throw()
		{ _Alloc_traits::deallocate(_M_get_allocator(), _M_data(), __size + 1); }
		
		// _M_construct_aux is used to implement the 21.3.1 para 15 which
		// requires special behaviour if _InIterator is an integral type
		template<typename _InIterator>
		void
		_M_construct_aux(_InIterator __beg, _InIterator __end,
			std::__false_type)
		{
			typedef typename iterator_traits<_InIterator>::iterator_category _Tag;
			_M_construct(__beg, __end, _Tag());
		}
		
		// _GLIBCXX_RESOLVE_LIB_DEFECTS
		// 438. Ambiguity in the "do the right thing" clause
		template<typename _Integer>
		void
		_M_construct_aux(_Integer __beg, _Integer __end, std::__true_type)
		{ _M_construct_aux_2(static_cast<size_type>(__beg), __end); }
		
		void
		_M_construct_aux_2(size_type __req, _CharT __c)
		{ _M_construct(__req, __c); }
		
		template<typename _InIterator>
		void
		_M_construct(_InIterator __beg, _InIterator __end)
		{
			typedef typename std::__is_integer<_InIterator>::__type _Integral;
			_M_construct_aux(__beg, __end, _Integral());
		}
		
		// For Input Iterators, used in istreambuf_iterators, etc.
		template<typename _InIterator>
		void
		_M_construct(_InIterator __beg, _InIterator __end,
			std::input_iterator_tag);
		
		// For forward_iterators up to random_access_iterators, used for
		// string::iterator, _CharT*, etc.
		template<typename _FwdIterator>
		void
		_M_construct(_FwdIterator __beg, _FwdIterator __end,
			std::forward_iterator_tag);
		
		void
		_M_construct(size_type __req, _CharT __c);
		
		allocator_type&
		_M_get_allocator()
		{ return _M_dataplus; }
		
		const allocator_type&
		_M_get_allocator() const
		{ return _M_dataplus; }
		
	private:
		
#ifdef _GLIBCXX_DISAMBIGUATE_REPLACE_INST
		// The explicit instantiations in misc-inst.cc require this due to
		// https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64063
		template<typename _Tp, bool _Requires =
		!__are_same<_Tp, _CharT*>::__value
		&& !__are_same<_Tp, const _CharT*>::__value
		&& !__are_same<_Tp, iterator>::__value
		&& !__are_same<_Tp, const_iterator>::__value>
		struct __enable_if_not_native_iterator
		{ typedef basic_string& __type; };
		template<typename _Tp>
		struct __enable_if_not_native_iterator<_Tp, false> { };
#endif
		
		size_type
		_M_check(size_type __pos, const char* __s) const
		{
			if (__pos > this->size())
				__throw_out_of_range_fmt(__N("%s: __pos (which is %zu) > "
					"this->size() (which is %zu)"),
					__s, __pos, this->size());
			return __pos;
		}
		
		void
		_M_check_length(size_type __n1, size_type __n2, const char* __s) const
		{
			if (this->max_size() - (this->size() - __n1) < __n2)
				__throw_length_error(__N(__s));
		}
		
		
		// NB: _M_limit doesn't check for a bad __pos value.
		size_type
		_M_limit(size_type __pos, size_type __off) const _GLIBCXX_NOEXCEPT
		{
			const bool __testoff =  __off < this->size() - __pos;
			return __testoff ? __off : this->size() - __pos;
		}
		
		// True if _Rep and source do not overlap.
		bool
		_M_disjunct(const _CharT* __s) const _GLIBCXX_NOEXCEPT
		{
			return (less<const _CharT*>()(__s, _M_data())
				|| less<const _CharT*>()(_M_data() + this->size(), __s));
		}
		
		// When __n = 1 way faster than the general multichar
		// traits_type::copy/move/assign.
		static void
		_S_copy(_CharT* __d, const _CharT* __s, size_type __n)
		{
			if (__n == 1)
				traits_type::assign(*__d, *__s);
			else
				traits_type::copy(__d, __s, __n);
		}
		
		static void
		_S_move(_CharT* __d, const _CharT* __s, size_type __n)
		{
			if (__n == 1)
				traits_type::assign(*__d, *__s);
			else
				traits_type::move(__d, __s, __n);
		}
		
		static void
		_S_assign(_CharT* __d, size_type __n, _CharT __c)
		{
			if (__n == 1)
				traits_type::assign(*__d, __c);
			else
				traits_type::assign(__d, __n, __c);
		}
		
		// _S_copy_chars is a separate template to permit specialization
		// to optimize for the common case of pointers as iterators.
		template<class _Iterator>
		static void
		_S_copy_chars(_CharT* __p, _Iterator __k1, _Iterator __k2)
		{
			for (; __k1 != __k2; ++__k1, (void)++__p)
				traits_type::assign(*__p, *__k1); // These types are off.
		}
		
		static void
		_S_copy_chars(_CharT* __p, iterator __k1, iterator __k2) _GLIBCXX_NOEXCEPT
		{ _S_copy_chars(__p, __k1.base(), __k2.base()); }
		
		static void
		_S_copy_chars(_CharT* __p, const_iterator __k1, const_iterator __k2)
		_GLIBCXX_NOEXCEPT
		{ _S_copy_chars(__p, __k1.base(), __k2.base()); }
		
		static void
		_S_copy_chars(_CharT* __p, _CharT* __k1, _CharT* __k2) _GLIBCXX_NOEXCEPT
		{ _S_copy(__p, __k1, __k2 - __k1); }
		
		static void
		_S_copy_chars(_CharT* __p, const _CharT* __k1, const _CharT* __k2)
		_GLIBCXX_NOEXCEPT
		{ _S_copy(__p, __k1, __k2 - __k1); }
		
		static int
		_S_compare(size_type __n1, size_type __n2) _GLIBCXX_NOEXCEPT
		{
			const difference_type __d = difference_type(__n1 - __n2);
			
			if (__d > __gnu_cxx::__numeric_traits<int>::__max)
				return __gnu_cxx::__numeric_traits<int>::__max;
			else if (__d < __gnu_cxx::__numeric_traits<int>::__min)
				return __gnu_cxx::__numeric_traits<int>::__min;
			else
				return int(__d);
		}
		
		void
		_M_assign(const basic_string&);
		
		void
		_M_mutate(size_type __pos, size_type __len1, const _CharT* __s,
			size_type __len2);
		
		void
		_M_erase(size_type __pos, size_type __n);
		
	public:
		// Construct/copy/destroy:
		// NB: We overload ctors in some cases instead of using default
		// arguments, per 17.4.4.4 para. 2 item 2.
		
		/**
		 *  @brief  Default constructor creates an empty string.
		 */
		basic_string()
		_GLIBCXX_NOEXCEPT_IF(is_nothrow_default_constructible<_Alloc>::value)
		: _M_dataplus(_M_local_data())
		{ _M_set_length(0); }
		
		/**
		 *  @brief  Construct an empty string using allocator @a a.
		 */
		explicit
		basic_string(const _Alloc& __a) _GLIBCXX_NOEXCEPT
		: _M_dataplus(_M_local_data(), __a)
		{ _M_set_length(0); }
		
		/**
		 *  @brief  Construct string with copy of value of @a __str.
		 *  @param  __str  Source string.
		 */
		basic_string(const basic_string& __str)
		: _M_dataplus(_M_local_data(),
			_Alloc_traits::_S_select_on_copy(__str._M_get_allocator()))
		{ _M_construct(__str._M_data(), __str._M_data() + __str.length()); }
		
		// _GLIBCXX_RESOLVE_LIB_DEFECTS
		// 2583. no way to supply an allocator for basic_string(str, pos)
		/**
		 *  @brief  Construct string as copy of a substring.
		 *  @param  __str  Source string.
		 *  @param  __pos  Index of first character to copy from.
		 *  @param  __a  Allocator to use.
		 */
		basic_string(const basic_string& __str, size_type __pos,
			const _Alloc& __a = _Alloc())
		: _M_dataplus(_M_local_data(), __a)
		{
			const _CharT* __start = __str._M_data()
			+ __str._M_check(__pos, "basic_string::basic_string");
			_M_construct(__start, __start + __str._M_limit(__pos, npos));
		}
		
		/**
		 *  @brief  Construct string as copy of a substring.
		 *  @param  __str  Source string.
		 *  @param  __pos  Index of first character to copy from.
		 *  @param  __n  Number of characters to copy.
		 */
		basic_string(const basic_string& __str, size_type __pos,
			size_type __n)
		: _M_dataplus(_M_local_data())
		{
			const _CharT* __start = __str._M_data()
			+ __str._M_check(__pos, "basic_string::basic_string");
			_M_construct(__start, __start + __str._M_limit(__pos, __n));
		}
		
		/**
		 *  @brief  Construct string as copy of a substring.
		 *  @param  __str  Source string.
		 *  @param  __pos  Index of first character to copy from.
		 *  @param  __n  Number of characters to copy.
		 *  @param  __a  Allocator to use.
		 */
		basic_string(const basic_string& __str, size_type __pos,
			size_type __n, const _Alloc& __a)
		: _M_dataplus(_M_local_data(), __a)
		{
			const _CharT* __start
			= __str._M_data() + __str._M_check(__pos, "string::string");
			_M_construct(__start, __start + __str._M_limit(__pos, __n));
		}
		
		/**
		 *  @brief  Construct string initialized by a character %array.
		 *  @param  __s  Source character %array.
		 *  @param  __n  Number of characters to copy.
		 *  @param  __a  Allocator to use (default is default allocator).
		 *
		 *  NB: @a __s must have at least @a __n characters, &apos;\\0&apos;
		 *  has no special meaning.
		 */
		basic_string(const _CharT* __s, size_type __n,
			const _Alloc& __a = _Alloc())
		: _M_dataplus(_M_local_data(), __a)
		{ _M_construct(__s, __s + __n); }
		
		/**
		 *  @brief  Construct string as copy of a C string.
		 *  @param  __s  Source C string.
		 *  @param  __a  Allocator to use (default is default allocator).
		 */
#if __cpp_deduction_guides && ! defined _GLIBCXX_DEFINING_STRING_INSTANTIATIONS
		// _GLIBCXX_RESOLVE_LIB_DEFECTS
		// 3076. basic_string CTAD ambiguity
		template<typename = _RequireAllocator<_Alloc>>
#endif
		basic_string(const _CharT* __s, const _Alloc& __a = _Alloc())
		: _M_dataplus(_M_local_data(), __a)
		{
			const _CharT* __end = __s ? __s + traits_type::length(__s)
			// We just need a non-null pointer here to get an exception:
			: reinterpret_cast<const _CharT*>(__alignof__(_CharT));
			_M_construct(__s, __end, random_access_iterator_tag());
		}
		
		/**
		 *  @brief  Construct string as multiple characters.
		 *  @param  __n  Number of characters.
		 *  @param  __c  Character to use.
		 *  @param  __a  Allocator to use (default is default allocator).
		 */
#if __cpp_deduction_guides && ! defined _GLIBCXX_DEFINING_STRING_INSTANTIATIONS
		// _GLIBCXX_RESOLVE_LIB_DEFECTS
		// 3076. basic_string CTAD ambiguity
		template<typename = _RequireAllocator<_Alloc>>
#endif
		basic_string(size_type __n, _CharT __c, const _Alloc& __a = _Alloc())
		: _M_dataplus(_M_local_data(), __a)
		{ _M_construct(__n, __c); }
		
#if __cplusplus >= 201103L
		/**
		 *  @brief  Move construct string.
		 *  @param  __str  Source string.
		 *
		 *  The newly-created string contains the exact contents of @a __str.
		 *  @a __str is a valid, but unspecified string.
		 */
		basic_string(basic_string&& __str) noexcept
		: _M_dataplus(_M_local_data(), std::move(__str._M_get_allocator()))
		{
			if (__str._M_is_local())
			{
				traits_type::copy(_M_local_buf, __str._M_local_buf,
					_S_local_capacity + 1);
			}
			else
			{
				_M_data(__str._M_data());
				_M_capacity(__str._M_allocated_capacity);
			}
			
			// Must use _M_length() here not _M_set_length() because
			// basic_stringbuf relies on writing into unallocated capacity so
			// we mess up the contents if we put a '\0' in the string.
			_M_length(__str.length());
			__str._M_data(__str._M_local_data());
			__str._M_set_length(0);
		}
		
		/**
		 *  @brief  Construct string from an initializer %list.
		 *  @param  __l  std::initializer_list of characters.
		 *  @param  __a  Allocator to use (default is default allocator).
		 */
		basic_string(initializer_list<_CharT> __l, const _Alloc& __a = _Alloc())
		: _M_dataplus(_M_local_data(), __a)
		{ _M_construct(__l.begin(), __l.end()); }
		
		basic_string(const basic_string& __str, const _Alloc& __a)
		: _M_dataplus(_M_local_data(), __a)
		{ _M_construct(__str.begin(), __str.end()); }
		
		basic_string(basic_string&& __str, const _Alloc& __a)
		noexcept(_Alloc_traits::_S_always_equal())
		: _M_dataplus(_M_local_data(), __a)
		{
			if (__str._M_is_local())
			{
				traits_type::copy(_M_local_buf, __str._M_local_buf,
					_S_local_capacity + 1);
				_M_length(__str.length());
				__str._M_set_length(0);
			}
			else if (_Alloc_traits::_S_always_equal()
				|| __str.get_allocator() == __a)
			{
				_M_data(__str._M_data());
				_M_length(__str.length());
				_M_capacity(__str._M_allocated_capacity);
				__str._M_data(__str._M_local_buf);
				__str._M_set_length(0);
			}
			else
				_M_construct(__str.begin(), __str.end());
		}
		
#endif // C++11
		
		/**
		 *  @brief  Construct string as copy of a range.
		 *  @param  __beg  Start of range.
		 *  @param  __end  End of range.
		 *  @param  __a  Allocator to use (default is default allocator).
		 */
#if __cplusplus >= 201103L
		template<typename _InputIterator,
		typename = std::_RequireInputIter<_InputIterator>>
#else
		template<typename _InputIterator>
#endif
		basic_string(_InputIterator __beg, _InputIterator __end,
			const _Alloc& __a = _Alloc())
		: _M_dataplus(_M_local_data(), __a)
		{ _M_construct(__beg, __end); }
		
#if __cplusplus >= 201703L
		/**
		 *  @brief  Construct string from a substring of a string_view.
		 *  @param  __t   Source object convertible to string view.
		 *  @param  __pos The index of the first character to copy from __t.
		 *  @param  __n   The number of characters to copy from __t.
		 *  @param  __a   Allocator to use.
		 */
		template<typename _Tp,
		typename = enable_if_t<is_convertible_v<const _Tp&, __sv_type>>>
		basic_string(const _Tp& __t, size_type __pos, size_type __n,
			const _Alloc& __a = _Alloc())
		: basic_string(_S_to_string_view(__t).substr(__pos, __n), __a) { }
		
		/**
		 *  @brief  Construct string from a string_view.
		 *  @param  __t  Source object convertible to string view.
		 *  @param  __a  Allocator to use (default is default allocator).
		 */
		template<typename _Tp, typename = _If_sv<_Tp, void>>
		explicit
		basic_string(const _Tp& __t, const _Alloc& __a = _Alloc())
		: basic_string(__sv_wrapper(_S_to_string_view(__t)), __a) { }
#endif // C++17
		
		/**
		 *  @brief  Destroy the string instance.
		 */
		~basic_string()
		{ _M_dispose(); }
		
		/**
		 *  @brief  Assign the value of @a str to this string.
		 *  @param  __str  Source string.
		 */
		basic_string&
		operator=(const basic_string& __str)
		{
			return this->assign(__str);
		}
		
		/**
		 *  @brief  Copy contents of @a s into this string.
		 *  @param  __s  Source null-terminated string.
		 */
		basic_string&
		operator=(const _CharT* __s)
		{ return this->assign(__s); }
		
		/**
		 *  @brief  Set value to string of length 1.
		 *  @param  __c  Source character.
		 *
		 *  Assigning to a character makes this string length 1 and
		 *  (*this)[0] == @a c.
		 */
		basic_string&
		operator=(_CharT __c)
		{
			this->assign(1, __c);
			return *this;
		}
		
#if __cplusplus >= 201103L
		/**
		 *  @brief  Move assign the value of @a str to this string.
		 *  @param  __str  Source string.
		 *
		 *  The contents of @a str are moved into this string (without copying).
		 *  @a str is a valid, but unspecified string.
		 */
		// _GLIBCXX_RESOLVE_LIB_DEFECTS
		// 2063. Contradictory requirements for string move assignment
		basic_string&
		operator=(basic_string&& __str)
		noexcept(_Alloc_traits::_S_nothrow_move())
		{
			if (!_M_is_local() && _Alloc_traits::_S_propagate_on_move_assign()
				&& !_Alloc_traits::_S_always_equal()
				&& _M_get_allocator() != __str._M_get_allocator())
			{
				// Destroy existing storage before replacing allocator.
				_M_destroy(_M_allocated_capacity);
				_M_data(_M_local_data());
				_M_set_length(0);
			}
			// Replace allocator if POCMA is true.
			std::__alloc_on_move(_M_get_allocator(), __str._M_get_allocator());
			
			if (__str._M_is_local())
			{
				// We've always got room for a short string, just copy it
				// (unless this is a self-move, because that would violate the
				// char_traits::copy precondition that the ranges don't overlap).
				if (__builtin_expect(std::__addressof(__str) != this, true))
				{
					if (__str.size())
						this->_S_copy(_M_data(), __str._M_data(), __str.size());
					_M_set_length(__str.size());
				}
			}
			else if (_Alloc_traits::_S_propagate_on_move_assign()
				|| _Alloc_traits::_S_always_equal()
				|| _M_get_allocator() == __str._M_get_allocator())
			{
				// Just move the allocated pointer, our allocator can free it.
				pointer __data = nullptr;
				size_type __capacity;
				if (!_M_is_local())
				{
					if (_Alloc_traits::_S_always_equal())
					{
						// __str can reuse our existing storage.
						__data = _M_data();
						__capacity = _M_allocated_capacity;
					}
					else // __str can't use it, so free it.
						_M_destroy(_M_allocated_capacity);
				}
				
				_M_data(__str._M_data());
				_M_length(__str.length());
				_M_capacity(__str._M_allocated_capacity);
				if (__data)
				{
					__str._M_data(__data);
					__str._M_capacity(__capacity);
				}
				else
					__str._M_data(__str._M_local_buf);
			}
			else // Need to do a deep copy
				assign(__str);
			__str.clear();
			return *this;
		}
		
		/**
		 *  @brief  Set value to string constructed from initializer %list.
		 *  @param  __l  std::initializer_list.
		 */
		basic_string&
		operator=(initializer_list<_CharT> __l)
		{
			this->assign(__l.begin(), __l.size());
			return *this;
		}
#endif // C++11
		
#if __cplusplus >= 201703L
		/**
		 *  @brief  Set value to string constructed from a string_view.
		 *  @param  __svt  An object convertible to string_view.
		 */
		template<typename _Tp>
		_If_sv<_Tp, basic_string&>
		operator=(const _Tp& __svt)
		{ return this->assign(__svt); }
		
		/**
		 *  @brief  Convert to a string_view.
		 *  @return A string_view.
		 */
		operator __sv_type() const noexcept
		{ return __sv_type(data(), size()); }
#endif // C++17
		
		// Iterators:
		/**
		 *  Returns a read/write iterator that points to the first character in
		 *  the %string.
		 */
		iterator
		begin() _GLIBCXX_NOEXCEPT
		{ return iterator(_M_data()); }
		
		/**
		 *  Returns a read-only (constant) iterator that points to the first
		 *  character in the %string.
		 */
		const_iterator
		begin() const _GLIBCXX_NOEXCEPT
		{ return const_iterator(_M_data()); }
		
		/**
		 *  Returns a read/write iterator that points one past the last
		 *  character in the %string.
		 */
		iterator
		end() _GLIBCXX_NOEXCEPT
		{ return iterator(_M_data() + this->size()); }
		
		/**
		 *  Returns a read-only (constant) iterator that points one past the
		 *  last character in the %string.
		 */
		const_iterator
		end() const _GLIBCXX_NOEXCEPT
		{ return const_iterator(_M_data() + this->size()); }
		
		/**
		 *  Returns a read/write reverse iterator that points to the last
		 *  character in the %string.  Iteration is done in reverse element
		 *  order.
		 */
		reverse_iterator
		rbegin() _GLIBCXX_NOEXCEPT
		{ return reverse_iterator(this->end()); }
		
		/**
		 *  Returns a read-only (constant) reverse iterator that points
		 *  to the last character in the %string.  Iteration is done in
		 *  reverse element order.
		 */
		const_reverse_iterator
		rbegin() const _GLIBCXX_NOEXCEPT
		{ return const_reverse_iterator(this->end()); }
		
		/**
		 *  Returns a read/write reverse iterator that points to one before the
		 *  first character in the %string.  Iteration is done in reverse
		 *  element order.
		 */
		reverse_iterator
		rend() _GLIBCXX_NOEXCEPT
		{ return reverse_iterator(this->begin()); }
		
		/**
		 *  Returns a read-only (constant) reverse iterator that points
		 *  to one before the first character in the %string.  Iteration
		 *  is done in reverse element order.
		 */
		const_reverse_iterator
		rend() const _GLIBCXX_NOEXCEPT
		{ return const_reverse_iterator(this->begin()); }
		
#if __cplusplus >= 201103L
		/**
		 *  Returns a read-only (constant) iterator that points to the first
		 *  character in the %string.
		 */
		const_iterator
		cbegin() const noexcept
		{ return const_iterator(this->_M_data()); }
		
		/**
		 *  Returns a read-only (constant) iterator that points one past the
		 *  last character in the %string.
		 */
		const_iterator
		cend() const noexcept
		{ return const_iterator(this->_M_data() + this->size()); }
		
		/**
		 *  Returns a read-only (constant) reverse iterator that points
		 *  to the last character in the %string.  Iteration is done in
		 *  reverse element order.
		 */
		const_reverse_iterator
		crbegin() const noexcept
		{ return const_reverse_iterator(this->end()); }
		
		/**
		 *  Returns a read-only (constant) reverse iterator that points
		 *  to one before the first character in the %string.  Iteration
		 *  is done in reverse element order.
		 */
		const_reverse_iterator
		crend() const noexcept
		{ return const_reverse_iterator(this->begin()); }
#endif
		
	public:
		// Capacity:
		///  Returns the number of characters in the string, not including any
		///  null-termination.
		size_type
		size() const _GLIBCXX_NOEXCEPT
		{ return _M_string_length; }
		
		///  Returns the number of characters in the string, not including any
		///  null-termination.
		size_type
		length() const _GLIBCXX_NOEXCEPT
		{ return _M_string_length; }
		
		///  Returns the size() of the largest possible %string.
		size_type
		max_size() const _GLIBCXX_NOEXCEPT
		{ return (_Alloc_traits::max_size(_M_get_allocator()) - 1) / 2; }
		
		/**
		 *  @brief  Resizes the %string to the specified number of characters.
		 *  @param  __n  Number of characters the %string should contain.
		 *  @param  __c  Character to fill any new elements.
		 *
		 *  This function will %resize the %string to the specified
		 *  number of characters.  If the number is smaller than the
		 *  %string's current size the %string is truncated, otherwise
		 *  the %string is extended and new elements are %set to @a __c.
		 */
		void
		resize(size_type __n, _CharT __c);
		
		/**
		 *  @brief  Resizes the %string to the specified number of characters.
		 *  @param  __n  Number of characters the %string should contain.
		 *
		 *  This function will resize the %string to the specified length.  If
		 *  the new size is smaller than the %string's current size the %string
		 *  is truncated, otherwise the %string is extended and new characters
		 *  are default-constructed.  For basic types such as char, this means
		 *  setting them to 0.
		 */
		void
		resize(size_type __n)
		{ this->resize(__n, _CharT()); }
		
#if __cplusplus >= 201103L
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
		///  A non-binding request to reduce capacity() to size().
		void
		shrink_to_fit() noexcept
		{ reserve(); }
#pragma GCC diagnostic pop
#endif
		
		/**
		 *  Returns the total number of characters that the %string can hold
		 *  before needing to allocate more memory.
		 */
		size_type
		capacity() const _GLIBCXX_NOEXCEPT
		{
			return _M_is_local() ? size_type(_S_local_capacity)
			: _M_allocated_capacity;
		}
		
		/**
		 *  @brief  Attempt to preallocate enough memory for specified number of
		 *          characters.
		 *  @param  __res_arg  Number of characters required.
		 *  @throw  std::length_error  If @a __res_arg exceeds @c max_size().
		 *
		 *  This function attempts to reserve enough memory for the
		 *  %string to hold the specified number of characters.  If the
		 *  number requested is more than max_size(), length_error is
		 *  thrown.
		 *
		 *  The advantage of this function is that if optimal code is a
		 *  necessity and the user can determine the string length that will be
		 *  required, the user can reserve the memory in %advance, and thus
		 *  prevent a possible reallocation of memory and copying of %string
		 *  data.
		 */
		void
		reserve(size_type __res_arg);
		
		/**
		 *  Equivalent to shrink_to_fit().
		 */
#if __cplusplus > 201703L
		[[deprecated("use shrink_to_fit() instead")]]
#endif
		void
		reserve();
		
		/**
		 *  Erases the string, making it empty.
		 */
		void
		clear() _GLIBCXX_NOEXCEPT
		{ _M_set_length(0); }
		
		/**
		 *  Returns true if the %string is empty.  Equivalent to 
		 *  <code>*this == ""</code>.
		 */
		_GLIBCXX_NODISCARD bool
		empty() const _GLIBCXX_NOEXCEPT
		{ return this->size() == 0; }
		
		// Element access:
		/**
		 *  @brief  Subscript access to the data contained in the %string.
		 *  @param  __pos  The index of the character to access.
		 *  @return  Read-only (constant) reference to the character.
		 *
		 *  This operator allows for easy, array-style, data access.
		 *  Note that data access with this operator is unchecked and
		 *  out_of_range lookups are not defined. (For checked lookups
		 *  see at().)
		 */
		const_reference
		operator[] (size_type __pos) const _GLIBCXX_NOEXCEPT
		{
			__glibcxx_assert(__pos <= size());
			return _M_data()[__pos];
		}
		
		/**
		 *  @brief  Subscript access to the data contained in the %string.
		 *  @param  __pos  The index of the character to access.
		 *  @return  Read/write reference to the character.
		 *
		 *  This operator allows for easy, array-style, data access.
		 *  Note that data access with this operator is unchecked and
		 *  out_of_range lookups are not defined. (For checked lookups
		 *  see at().)
		 */
		reference
		operator[](size_type __pos)
		{
			// Allow pos == size() both in C++98 mode, as v3 extension,
			// and in C++11 mode.
			__glibcxx_assert(__pos <= size());
			// In pedantic mode be strict in C++98 mode.
			_GLIBCXX_DEBUG_PEDASSERT(__cplusplus >= 201103L || __pos < size());
			return _M_data()[__pos];
		}
		
		/**
		 *  @brief  Provides access to the data contained in the %string.
		 *  @param __n The index of the character to access.
		 *  @return  Read-only (const) reference to the character.
		 *  @throw  std::out_of_range  If @a n is an invalid index.
		 *
		 *  This function provides for safer data access.  The parameter is
		 *  first checked that it is in the range of the string.  The function
		 *  throws out_of_range if the check fails.
		 */
		const_reference
		at(size_type __n) const
		{
			if (__n >= this->size())
				__throw_out_of_range_fmt(__N("basic_string::at: __n "
					"(which is %zu) >= this->size() "
					"(which is %zu)"),
					__n, this->size());
			return _M_data()[__n];
		}
		
		/**
		 *  @brief  Provides access to the data contained in the %string.
		 *  @param __n The index of the character to access.
		 *  @return  Read/write reference to the character.
		 *  @throw  std::out_of_range  If @a n is an invalid index.
		 *
		 *  This function provides for safer data access.  The parameter is
		 *  first checked that it is in the range of the string.  The function
		 *  throws out_of_range if the check fails.
		 */
		reference
		at(size_type __n)
		{
			if (__n >= size())
				__throw_out_of_range_fmt(__N("basic_string::at: __n "
					"(which is %zu) >= this->size() "
					"(which is %zu)"),
					__n, this->size());
			return _M_data()[__n];
		}
		
#if __cplusplus >= 201103L
		/**
		 *  Returns a read/write reference to the data at the first
		 *  element of the %string.
		 */
		reference
		front() noexcept
		{
			__glibcxx_assert(!empty());
			return operator[](0);
		}
		
		/**
		 *  Returns a read-only (constant) reference to the data at the first
		 *  element of the %string.
		 */
		const_reference
		front() const noexcept
		{
			__glibcxx_assert(!empty());
			return operator[](0);
		}
		
		/**
		 *  Returns a read/write reference to the data at the last
		 *  element of the %string.
		 */
		reference
		back() noexcept
		{
			__glibcxx_assert(!empty());
			return operator[](this->size() - 1);
		}
		
		/**
		 *  Returns a read-only (constant) reference to the data at the
		 *  last element of the %string.
		 */
		const_reference
		back() const noexcept
		{
			__glibcxx_assert(!empty());
			return operator[](this->size() - 1);
		}
#endif
		
		// Modifiers:
		/**
		 *  @brief  Append a string to this string.
		 *  @param __str  The string to append.
		 *  @return  Reference to this string.
		 */
		basic_string&
		operator+=(const basic_string& __str)
		{ return this->append(__str); }
		
		/**
		 *  @brief  Append a C string.
		 *  @param __s  The C string to append.
		 *  @return  Reference to this string.
		 */
		basic_string&
		operator+=(const _CharT* __s)
		{ return this->append(__s); }
		
		/**
		 *  @brief  Append a character.
		 *  @param __c  The character to append.
		 *  @return  Reference to this string.
		 */
		basic_string&
		operator+=(_CharT __c)
		{
			this->push_back(__c);
			return *this;
		}
		
#if __cplusplus >= 201103L
		/**
		 *  @brief  Append an initializer_list of characters.
		 *  @param __l  The initializer_list of characters to be appended.
		 *  @return  Reference to this string.
		 */
		basic_string&
		operator+=(initializer_list<_CharT> __l)
		{ return this->append(__l.begin(), __l.size()); }
#endif // C++11
		
#if __cplusplus >= 201703L
		/**
		 *  @brief  Append a string_view.
		 *  @param __svt  An object convertible to string_view to be appended.
		 *  @return  Reference to this string.
		 */
		template<typename _Tp>
		_If_sv<_Tp, basic_string&>
		operator+=(const _Tp& __svt)
		{ return this->append(__svt); }
#endif // C++17
		
		/**
		 *  @brief  Append a string to this string.
		 *  @param __str  The string to append.
		 *  @return  Reference to this string.
		 */
		basic_string&
		append(const basic_string& __str)
		{ return _M_append(__str._M_data(), __str.size()); }
		
		/**
		 *  @brief  Append a substring.
		 *  @param __str  The string to append.
		 *  @param __pos  Index of the first character of str to append.
		 *  @param __n  The number of characters to append.
		 *  @return  Reference to this string.
		 *  @throw  std::out_of_range if @a __pos is not a valid index.
		 *
		 *  This function appends @a __n characters from @a __str
		 *  starting at @a __pos to this string.  If @a __n is is larger
		 *  than the number of available characters in @a __str, the
		 *  remainder of @a __str is appended.
		 */
		basic_string&
		append(const basic_string& __str, size_type __pos, size_type __n = npos)
		{ return _M_append(__str._M_data()
			+ __str._M_check(__pos, "basic_string::append"),
			__str._M_limit(__pos, __n)); }
		
		/**
		 *  @brief  Append a C substring.
		 *  @param __s  The C string to append.
		 *  @param __n  The number of characters to append.
		 *  @return  Reference to this string.
		 */
		basic_string&
		append(const _CharT* __s, size_type __n)
		{
			__glibcxx_requires_string_len(__s, __n);
			_M_check_length(size_type(0), __n, "basic_string::append");
			return _M_append(__s, __n);
		}
		
		/**
		 *  @brief  Append a C string.
		 *  @param __s  The C string to append.
		 *  @return  Reference to this string.
		 */
		basic_string&
		append(const _CharT* __s)
		{
			__glibcxx_requires_string(__s);
			const size_type __n = traits_type::length(__s);
			_M_check_length(size_type(0), __n, "basic_string::append");
			return _M_append(__s, __n);
		}
		
		/**
		 *  @brief  Append multiple characters.
		 *  @param __n  The number of characters to append.
		 *  @param __c  The character to use.
		 *  @return  Reference to this string.
		 *
		 *  Appends __n copies of __c to this string.
		 */
		basic_string&
		append(size_type __n, _CharT __c)
		{ return _M_replace_aux(this->size(), size_type(0), __n, __c); }
		
#if __cplusplus >= 201103L
		/**
		 *  @brief  Append an initializer_list of characters.
		 *  @param __l  The initializer_list of characters to append.
		 *  @return  Reference to this string.
		 */
		basic_string&
		append(initializer_list<_CharT> __l)
		{ return this->append(__l.begin(), __l.size()); }
#endif // C++11
		
		/**
		 *  @brief  Append a range of characters.
		 *  @param __first  Iterator referencing the first character to append.
		 *  @param __last  Iterator marking the end of the range.
		 *  @return  Reference to this string.
		 *
		 *  Appends characters in the range [__first,__last) to this string.
		 */
#if __cplusplus >= 201103L
		template<class _InputIterator,
		typename = std::_RequireInputIter<_InputIterator>>
#else
		template<class _InputIterator>
#endif
		basic_string&
		append(_InputIterator __first, _InputIterator __last)
		{ return this->replace(end(), end(), __first, __last); }
		
#if __cplusplus >= 201703L
		/**
		 *  @brief  Append a string_view.
		 *  @param __svt  An object convertible to string_view to be appended.
		 *  @return  Reference to this string.
		 */
		template<typename _Tp>
		_If_sv<_Tp, basic_string&>
		append(const _Tp& __svt)
		{
			__sv_type __sv = __svt;
			return this->append(__sv.data(), __sv.size());
		}
		
		/**
		 *  @brief  Append a range of characters from a string_view.
		 *  @param __svt  An object convertible to string_view to be appended from.
		 *  @param __pos The position in the string_view to append from.
		 *  @param __n   The number of characters to append from the string_view.
		 *  @return  Reference to this string.
		 */
		template<typename _Tp>
		_If_sv<_Tp, basic_string&>
		append(const _Tp& __svt, size_type __pos, size_type __n = npos)
		{
			__sv_type __sv = __svt;
			return _M_append(__sv.data()
				+ std::__sv_check(__sv.size(), __pos, "basic_string::append"),
				std::__sv_limit(__sv.size(), __pos, __n));
		}
#endif // C++17
		
		/**
		 *  @brief  Append a single character.
		 *  @param __c  Character to append.
		 */
		void
		push_back(_CharT __c)
		{
			const size_type __size = this->size();
			if (__size + 1 > this->capacity())
				this->_M_mutate(__size, size_type(0), 0, size_type(1));
			traits_type::assign(this->_M_data()[__size], __c);
			this->_M_set_length(__size + 1);
		}
		
		/**
		 *  @brief  Set value to contents of another string.
		 *  @param  __str  Source string to use.
		 *  @return  Reference to this string.
		 */
		basic_string&
		assign(const basic_string& __str)
		{
#if __cplusplus >= 201103L
			if (_Alloc_traits::_S_propagate_on_copy_assign())
			{
				if (!_Alloc_traits::_S_always_equal() && !_M_is_local()
					&& _M_get_allocator() != __str._M_get_allocator())
				{
					// Propagating allocator cannot free existing storage so must
					// deallocate it before replacing current allocator.
					if (__str.size() <= _S_local_capacity)
					{
						_M_destroy(_M_allocated_capacity);
						_M_data(_M_local_data());
						_M_set_length(0);
					}
					else
					{
						const auto __len = __str.size();
						auto __alloc = __str._M_get_allocator();
						// If this allocation throws there are no effects:
						auto __ptr = _Alloc_traits::allocate(__alloc, __len + 1);
						_M_destroy(_M_allocated_capacity);
						_M_data(__ptr);
						_M_capacity(__len);
						_M_set_length(__len);
					}
				}
				std::__alloc_on_copy(_M_get_allocator(), __str._M_get_allocator());
			}
#endif
			this->_M_assign(__str);
			return *this;
		}
		
#if __cplusplus >= 201103L
		/**
		 *  @brief  Set value to contents of another string.
		 *  @param  __str  Source string to use.
		 *  @return  Reference to this string.
		 *
		 *  This function sets this string to the exact contents of @a __str.
		 *  @a __str is a valid, but unspecified string.
		 */
		basic_string&
		assign(basic_string&& __str)
		noexcept(_Alloc_traits::_S_nothrow_move())
		{
			// _GLIBCXX_RESOLVE_LIB_DEFECTS
			// 2063. Contradictory requirements for string move assignment
			return *this = std::move(__str);
		}
#endif // C++11
		
		/**
		 *  @brief  Set value to a substring of a string.
		 *  @param __str  The string to use.
		 *  @param __pos  Index of the first character of str.
		 *  @param __n  Number of characters to use.
		 *  @return  Reference to this string.
		 *  @throw  std::out_of_range if @a pos is not a valid index.
		 *
		 *  This function sets this string to the substring of @a __str
		 *  consisting of @a __n characters at @a __pos.  If @a __n is
		 *  is larger than the number of available characters in @a
		 *  __str, the remainder of @a __str is used.
		 */
		basic_string&
		assign(const basic_string& __str, size_type __pos, size_type __n = npos)
		{ return _M_replace(size_type(0), this->size(), __str._M_data()
			+ __str._M_check(__pos, "basic_string::assign"),
			__str._M_limit(__pos, __n)); }
		
		/**
		 *  @brief  Set value to a C substring.
		 *  @param __s  The C string to use.
		 *  @param __n  Number of characters to use.
		 *  @return  Reference to this string.
		 *
		 *  This function sets the value of this string to the first @a __n
		 *  characters of @a __s.  If @a __n is is larger than the number of
		 *  available characters in @a __s, the remainder of @a __s is used.
		 */
		basic_string&
		assign(const _CharT* __s, size_type __n)
		{
			__glibcxx_requires_string_len(__s, __n);
			return _M_replace(size_type(0), this->size(), __s, __n);
		}
		
		/**
		 *  @brief  Set value to contents of a C string.
		 *  @param __s  The C string to use.
		 *  @return  Reference to this string.
		 *
		 *  This function sets the value of this string to the value of @a __s.
		 *  The data is copied, so there is no dependence on @a __s once the
		 *  function returns.
		 */
		basic_string&
		assign(const _CharT* __s)
		{
			__glibcxx_requires_string(__s);
			return _M_replace(size_type(0), this->size(), __s,
				traits_type::length(__s));
		}
		
		/**
		 *  @brief  Set value to multiple characters.
		 *  @param __n  Length of the resulting string.
		 *  @param __c  The character to use.
		 *  @return  Reference to this string.
		 *
		 *  This function sets the value of this string to @a __n copies of
		 *  character @a __c.
		 */
		basic_string&
		assign(size_type __n, _CharT __c)
		{ return _M_replace_aux(size_type(0), this->size(), __n, __c); }
		
		/**
		 *  @brief  Set value to a range of characters.
		 *  @param __first  Iterator referencing the first character to append.
		 *  @param __last  Iterator marking the end of the range.
		 *  @return  Reference to this string.
		 *
		 *  Sets value of string to characters in the range [__first,__last).
		 */
#if __cplusplus >= 201103L
		template<class _InputIterator,
		typename = std::_RequireInputIter<_InputIterator>>
#else
		template<class _InputIterator>
#endif
		basic_string&
		assign(_InputIterator __first, _InputIterator __last)
		{ return this->replace(begin(), end(), __first, __last); }
		
#if __cplusplus >= 201103L
		/**
		 *  @brief  Set value to an initializer_list of characters.
		 *  @param __l  The initializer_list of characters to assign.
		 *  @return  Reference to this string.
		 */
		basic_string&
		assign(initializer_list<_CharT> __l)
		{ return this->assign(__l.begin(), __l.size()); }
#endif // C++11
		
#if __cplusplus >= 201703L
		/**
		 *  @brief  Set value from a string_view.
		 *  @param __svt  The source object convertible to string_view.
		 *  @return  Reference to this string.
		 */
		template<typename _Tp>
		_If_sv<_Tp, basic_string&>
		assign(const _Tp& __svt)
		{
			__sv_type __sv = __svt;
			return this->assign(__sv.data(), __sv.size());
		}
		
		/**
		 *  @brief  Set value from a range of characters in a string_view.
		 *  @param __svt  The source object convertible to string_view.
		 *  @param __pos  The position in the string_view to assign from.
		 *  @param __n  The number of characters to assign.
		 *  @return  Reference to this string.
		 */
		template<typename _Tp>
		_If_sv<_Tp, basic_string&>
		assign(const _Tp& __svt, size_type __pos, size_type __n = npos)
		{
			__sv_type __sv = __svt;
			return _M_replace(size_type(0), this->size(),
				__sv.data()
				+ std::__sv_check(__sv.size(), __pos, "basic_string::assign"),
				std::__sv_limit(__sv.size(), __pos, __n));
		}
#endif // C++17
		
#if __cplusplus >= 201103L
		/**
		 *  @brief  Insert multiple characters.
		 *  @param __p  Const_iterator referencing location in string to
		 *              insert at.
		 *  @param __n  Number of characters to insert
		 *  @param __c  The character to insert.
		 *  @return  Iterator referencing the first inserted char.
		 *  @throw  std::length_error  If new length exceeds @c max_size().
		 *
		 *  Inserts @a __n copies of character @a __c starting at the
		 *  position referenced by iterator @a __p.  If adding
		 *  characters causes the length to exceed max_size(),
		 *  length_error is thrown.  The value of the string doesn't
		 *  change if an error is thrown.
		 */
		iterator
		insert(const_iterator __p, size_type __n, _CharT __c)
		{
			_GLIBCXX_DEBUG_PEDASSERT(__p >= begin() && __p <= end());
			const size_type __pos = __p - begin();
			this->replace(__p, __p, __n, __c);
			return iterator(this->_M_data() + __pos);
		}
#else
		/**
		 *  @brief  Insert multiple characters.
		 *  @param __p  Iterator referencing location in string to insert at.
		 *  @param __n  Number of characters to insert
		 *  @param __c  The character to insert.
		 *  @throw  std::length_error  If new length exceeds @c max_size().
		 *
		 *  Inserts @a __n copies of character @a __c starting at the
		 *  position referenced by iterator @a __p.  If adding
		 *  characters causes the length to exceed max_size(),
		 *  length_error is thrown.  The value of the string doesn't
		 *  change if an error is thrown.
		 */
		void
		insert(iterator __p, size_type __n, _CharT __c)
		{	this->replace(__p, __p, __n, __c);  }
#endif
		
#if __cplusplus >= 201103L
		/**
		 *  @brief  Insert a range of characters.
		 *  @param __p  Const_iterator referencing location in string to
		 *              insert at.
		 *  @param __beg  Start of range.
		 *  @param __end  End of range.
		 *  @return  Iterator referencing the first inserted char.
		 *  @throw  std::length_error  If new length exceeds @c max_size().
		 *
		 *  Inserts characters in range [beg,end).  If adding characters
		 *  causes the length to exceed max_size(), length_error is
		 *  thrown.  The value of the string doesn't change if an error
		 *  is thrown.
		 */
		template<class _InputIterator,
		typename = std::_RequireInputIter<_InputIterator>>
		iterator
		insert(const_iterator __p, _InputIterator __beg, _InputIterator __end)
		{
			_GLIBCXX_DEBUG_PEDASSERT(__p >= begin() && __p <= end());
			const size_type __pos = __p - begin();
			this->replace(__p, __p, __beg, __end);
			return iterator(this->_M_data() + __pos);
		}
#else
		/**
		 *  @brief  Insert a range of characters.
		 *  @param __p  Iterator referencing location in string to insert at.
		 *  @param __beg  Start of range.
		 *  @param __end  End of range.
		 *  @throw  std::length_error  If new length exceeds @c max_size().
		 *
		 *  Inserts characters in range [__beg,__end).  If adding
		 *  characters causes the length to exceed max_size(),
		 *  length_error is thrown.  The value of the string doesn't
		 *  change if an error is thrown.
		 */
		template<class _InputIterator>
		void
		insert(iterator __p, _InputIterator __beg, _InputIterator __end)
		{ this->replace(__p, __p, __beg, __end); }
#endif
		
#if __cplusplus >= 201103L
		/**
		 *  @brief  Insert an initializer_list of characters.
		 *  @param __p  Iterator referencing location in string to insert at.
		 *  @param __l  The initializer_list of characters to insert.
		 *  @throw  std::length_error  If new length exceeds @c max_size().
		 */
		iterator
		insert(const_iterator __p, initializer_list<_CharT> __l)
		{ return this->insert(__p, __l.begin(), __l.end()); }
		
#ifdef _GLIBCXX_DEFINING_STRING_INSTANTIATIONS
		// See PR libstdc++/83328
		void
		insert(iterator __p, initializer_list<_CharT> __l)
		{
			_GLIBCXX_DEBUG_PEDASSERT(__p >= begin() && __p <= end());
			this->insert(__p - begin(), __l.begin(), __l.size());
		}
#endif
#endif // C++11
		
		/**
		 *  @brief  Insert value of a string.
		 *  @param __pos1 Position in string to insert at.
		 *  @param __str  The string to insert.
		 *  @return  Reference to this string.
		 *  @throw  std::length_error  If new length exceeds @c max_size().
		 *
		 *  Inserts value of @a __str starting at @a __pos1.  If adding
		 *  characters causes the length to exceed max_size(),
		 *  length_error is thrown.  The value of the string doesn't
		 *  change if an error is thrown.
		 */
		basic_string&
		insert(size_type __pos1, const basic_string& __str)
		{ return this->replace(__pos1, size_type(0),
			__str._M_data(), __str.size()); }
		
		/**
		 *  @brief  Insert a substring.
		 *  @param __pos1  Position in string to insert at.
		 *  @param __str   The string to insert.
		 *  @param __pos2  Start of characters in str to insert.
		 *  @param __n  Number of characters to insert.
		 *  @return  Reference to this string.
		 *  @throw  std::length_error  If new length exceeds @c max_size().
		 *  @throw  std::out_of_range  If @a pos1 > size() or
		 *  @a __pos2 > @a str.size().
		 *
		 *  Starting at @a pos1, insert @a __n character of @a __str
		 *  beginning with @a __pos2.  If adding characters causes the
		 *  length to exceed max_size(), length_error is thrown.  If @a
		 *  __pos1 is beyond the end of this string or @a __pos2 is
		 *  beyond the end of @a __str, out_of_range is thrown.  The
		 *  value of the string doesn't change if an error is thrown.
		 */
		basic_string&
		insert(size_type __pos1, const basic_string& __str,
			size_type __pos2, size_type __n = npos)
		{ return this->replace(__pos1, size_type(0), __str._M_data()
			+ __str._M_check(__pos2, "basic_string::insert"),
			__str._M_limit(__pos2, __n)); }
		
		/**
		 *  @brief  Insert a C substring.
		 *  @param __pos  Position in string to insert at.
		 *  @param __s  The C string to insert.
		 *  @param __n  The number of characters to insert.
		 *  @return  Reference to this string.
		 *  @throw  std::length_error  If new length exceeds @c max_size().
		 *  @throw  std::out_of_range  If @a __pos is beyond the end of this
		 *  string.
		 *
		 *  Inserts the first @a __n characters of @a __s starting at @a
		 *  __pos.  If adding characters causes the length to exceed
		 *  max_size(), length_error is thrown.  If @a __pos is beyond
		 *  end(), out_of_range is thrown.  The value of the string
		 *  doesn't change if an error is thrown.
		 */
		basic_string&
		insert(size_type __pos, const _CharT* __s, size_type __n)
		{ return this->replace(__pos, size_type(0), __s, __n); }
		
		/**
		 *  @brief  Insert a C string.
		 *  @param __pos  Position in string to insert at.
		 *  @param __s  The C string to insert.
		 *  @return  Reference to this string.
		 *  @throw  std::length_error  If new length exceeds @c max_size().
		 *  @throw  std::out_of_range  If @a pos is beyond the end of this
		 *  string.
		 *
		 *  Inserts the first @a n characters of @a __s starting at @a __pos.  If
		 *  adding characters causes the length to exceed max_size(),
		 *  length_error is thrown.  If @a __pos is beyond end(), out_of_range is
		 *  thrown.  The value of the string doesn't change if an error is
		 *  thrown.
		 */
		basic_string&
		insert(size_type __pos, const _CharT* __s)
		{
			__glibcxx_requires_string(__s);
			return this->replace(__pos, size_type(0), __s,
				traits_type::length(__s));
		}
		
		/**
		 *  @brief  Insert multiple characters.
		 *  @param __pos  Index in string to insert at.
		 *  @param __n  Number of characters to insert
		 *  @param __c  The character to insert.
		 *  @return  Reference to this string.
		 *  @throw  std::length_error  If new length exceeds @c max_size().
		 *  @throw  std::out_of_range  If @a __pos is beyond the end of this
		 *  string.
		 *
		 *  Inserts @a __n copies of character @a __c starting at index
		 *  @a __pos.  If adding characters causes the length to exceed
		 *  max_size(), length_error is thrown.  If @a __pos > length(),
		 *  out_of_range is thrown.  The value of the string doesn't
		 *  change if an error is thrown.
		 */
		basic_string&
		insert(size_type __pos, size_type __n, _CharT __c)
		{ return _M_replace_aux(_M_check(__pos, "basic_string::insert"),
			size_type(0), __n, __c); }
		
		/**
		 *  @brief  Insert one character.
		 *  @param __p  Iterator referencing position in string to insert at.
		 *  @param __c  The character to insert.
		 *  @return  Iterator referencing newly inserted char.
		 *  @throw  std::length_error  If new length exceeds @c max_size().
		 *
		 *  Inserts character @a __c at position referenced by @a __p.
		 *  If adding character causes the length to exceed max_size(),
		 *  length_error is thrown.  If @a __p is beyond end of string,
		 *  out_of_range is thrown.  The value of the string doesn't
		 *  change if an error is thrown.
		 */
		iterator
		insert(__const_iterator __p, _CharT __c)
		{
			_GLIBCXX_DEBUG_PEDASSERT(__p >= begin() && __p <= end());
			const size_type __pos = __p - begin();
			_M_replace_aux(__pos, size_type(0), size_type(1), __c);
			return iterator(_M_data() + __pos);
		}
		
#if __cplusplus >= 201703L
		/**
		 *  @brief  Insert a string_view.
		 *  @param __pos  Position in string to insert at.
		 *  @param __svt  The object convertible to string_view to insert.
		 *  @return  Reference to this string.
		 */
		template<typename _Tp>
		_If_sv<_Tp, basic_string&>
		insert(size_type __pos, const _Tp& __svt)
		{
			__sv_type __sv = __svt;
			return this->insert(__pos, __sv.data(), __sv.size());
		}
		
		/**
		 *  @brief  Insert a string_view.
		 *  @param __pos1  Position in string to insert at.
		 *  @param __svt   The object convertible to string_view to insert from.
		 *  @param __pos2  Start of characters in str to insert.
		 *  @param __n    The number of characters to insert.
		 *  @return  Reference to this string.
		 */
		template<typename _Tp>
		_If_sv<_Tp, basic_string&>
		insert(size_type __pos1, const _Tp& __svt,
			size_type __pos2, size_type __n = npos)
		{
			__sv_type __sv = __svt;
			return this->replace(__pos1, size_type(0),
				__sv.data()
				+ std::__sv_check(__sv.size(), __pos2, "basic_string::insert"),
				std::__sv_limit(__sv.size(), __pos2, __n));
		}
#endif // C++17
		
		/**
		 *  @brief  Remove characters.
		 *  @param __pos  Index of first character to remove (default 0).
		 *  @param __n  Number of characters to remove (default remainder).
		 *  @return  Reference to this string.
		 *  @throw  std::out_of_range  If @a pos is beyond the end of this
		 *  string.
		 *
		 *  Removes @a __n characters from this string starting at @a
		 *  __pos.  The length of the string is reduced by @a __n.  If
		 *  there are < @a __n characters to remove, the remainder of
		 *  the string is truncated.  If @a __p is beyond end of string,
		 *  out_of_range is thrown.  The value of the string doesn't
		 *  change if an error is thrown.
		 */
		basic_string&
		erase(size_type __pos = 0, size_type __n = npos)
		{
			_M_check(__pos, "basic_string::erase");
			if (__n == npos)
				this->_M_set_length(__pos);
			else if (__n != 0)
				this->_M_erase(__pos, _M_limit(__pos, __n));
			return *this;
		}
		
		/**
		 *  @brief  Remove one character.
		 *  @param __position  Iterator referencing the character to remove.
		 *  @return  iterator referencing same location after removal.
		 *
		 *  Removes the character at @a __position from this string. The value
		 *  of the string doesn't change if an error is thrown.
		 */
		iterator
		erase(__const_iterator __position)
		{
			_GLIBCXX_DEBUG_PEDASSERT(__position >= begin()
				&& __position < end());
			const size_type __pos = __position - begin();
			this->_M_erase(__pos, size_type(1));
			return iterator(_M_data() + __pos);
		}
		
		/**
		 *  @brief  Remove a range of characters.
		 *  @param __first  Iterator referencing the first character to remove.
		 *  @param __last  Iterator referencing the end of the range.
		 *  @return  Iterator referencing location of first after removal.
		 *
		 *  Removes the characters in the range [first,last) from this string.
		 *  The value of the string doesn't change if an error is thrown.
		 */
		iterator
		erase(__const_iterator __first, __const_iterator __last)
		{
			_GLIBCXX_DEBUG_PEDASSERT(__first >= begin() && __first <= __last
				&& __last <= end());
			const size_type __pos = __first - begin();
			if (__last == end())
				this->_M_set_length(__pos);
			else
				this->_M_erase(__pos, __last - __first);
			return iterator(this->_M_data() + __pos);
		}
		
#if __cplusplus >= 201103L
		/**
		 *  @brief  Remove the last character.
		 *
		 *  The string must be non-empty.
		 */
		void
		pop_back() noexcept
		{
			__glibcxx_assert(!empty());
			_M_erase(size() - 1, 1);
		}
#endif // C++11
		
		/**
		 *  @brief  Replace characters with value from another string.
		 *  @param __pos  Index of first character to replace.
		 *  @param __n  Number of characters to be replaced.
		 *  @param __str  String to insert.
		 *  @return  Reference to this string.
		 *  @throw  std::out_of_range  If @a pos is beyond the end of this
		 *  string.
		 *  @throw  std::length_error  If new length exceeds @c max_size().
		 *
		 *  Removes the characters in the range [__pos,__pos+__n) from
		 *  this string.  In place, the value of @a __str is inserted.
		 *  If @a __pos is beyond end of string, out_of_range is thrown.
		 *  If the length of the result exceeds max_size(), length_error
		 *  is thrown.  The value of the string doesn't change if an
		 *  error is thrown.
		 */
		basic_string&
		replace(size_type __pos, size_type __n, const basic_string& __str)
		{ return this->replace(__pos, __n, __str._M_data(), __str.size()); }
		
		/**
		 *  @brief  Replace characters with value from another string.
		 *  @param __pos1  Index of first character to replace.
		 *  @param __n1  Number of characters to be replaced.
		 *  @param __str  String to insert.
		 *  @param __pos2  Index of first character of str to use.
		 *  @param __n2  Number of characters from str to use.
		 *  @return  Reference to this string.
		 *  @throw  std::out_of_range  If @a __pos1 > size() or @a __pos2 >
		 *  __str.size().
		 *  @throw  std::length_error  If new length exceeds @c max_size().
		 *
		 *  Removes the characters in the range [__pos1,__pos1 + n) from this
		 *  string.  In place, the value of @a __str is inserted.  If @a __pos is
		 *  beyond end of string, out_of_range is thrown.  If the length of the
		 *  result exceeds max_size(), length_error is thrown.  The value of the
		 *  string doesn't change if an error is thrown.
		 */
		basic_string&
		replace(size_type __pos1, size_type __n1, const basic_string& __str,
			size_type __pos2, size_type __n2 = npos)
		{ return this->replace(__pos1, __n1, __str._M_data()
			+ __str._M_check(__pos2, "basic_string::replace"),
			__str._M_limit(__pos2, __n2)); }
		
		/**
		 *  @brief  Replace characters with value of a C substring.
		 *  @param __pos  Index of first character to replace.
		 *  @param __n1  Number of characters to be replaced.
		 *  @param __s  C string to insert.
		 *  @param __n2  Number of characters from @a s to use.
		 *  @return  Reference to this string.
		 *  @throw  std::out_of_range  If @a pos1 > size().
		 *  @throw  std::length_error  If new length exceeds @c max_size().
		 *
		 *  Removes the characters in the range [__pos,__pos + __n1)
		 *  from this string.  In place, the first @a __n2 characters of
		 *  @a __s are inserted, or all of @a __s if @a __n2 is too large.  If
		 *  @a __pos is beyond end of string, out_of_range is thrown.  If
		 *  the length of result exceeds max_size(), length_error is
		 *  thrown.  The value of the string doesn't change if an error
		 *  is thrown.
		 */
		basic_string&
		replace(size_type __pos, size_type __n1, const _CharT* __s,
			size_type __n2)
		{
			__glibcxx_requires_string_len(__s, __n2);
			return _M_replace(_M_check(__pos, "basic_string::replace"),
				_M_limit(__pos, __n1), __s, __n2);
		}
		
		/**
		 *  @brief  Replace characters with value of a C string.
		 *  @param __pos  Index of first character to replace.
		 *  @param __n1  Number of characters to be replaced.
		 *  @param __s  C string to insert.
		 *  @return  Reference to this string.
		 *  @throw  std::out_of_range  If @a pos > size().
		 *  @throw  std::length_error  If new length exceeds @c max_size().
		 *
		 *  Removes the characters in the range [__pos,__pos + __n1)
		 *  from this string.  In place, the characters of @a __s are
		 *  inserted.  If @a __pos is beyond end of string, out_of_range
		 *  is thrown.  If the length of result exceeds max_size(),
		 *  length_error is thrown.  The value of the string doesn't
		 *  change if an error is thrown.
		 */
		basic_string&
		replace(size_type __pos, size_type __n1, const _CharT* __s)
		{
			__glibcxx_requires_string(__s);
			return this->replace(__pos, __n1, __s, traits_type::length(__s));
		}
		
		/**
		 *  @brief  Replace characters with multiple characters.
		 *  @param __pos  Index of first character to replace.
		 *  @param __n1  Number of characters to be replaced.
		 *  @param __n2  Number of characters to insert.
		 *  @param __c  Character to insert.
		 *  @return  Reference to this string.
		 *  @throw  std::out_of_range  If @a __pos > size().
		 *  @throw  std::length_error  If new length exceeds @c max_size().
		 *
		 *  Removes the characters in the range [pos,pos + n1) from this
		 *  string.  In place, @a __n2 copies of @a __c are inserted.
		 *  If @a __pos is beyond end of string, out_of_range is thrown.
		 *  If the length of result exceeds max_size(), length_error is
		 *  thrown.  The value of the string doesn't change if an error
		 *  is thrown.
		 */
		basic_string&
		replace(size_type __pos, size_type __n1, size_type __n2, _CharT __c)
		{ return _M_replace_aux(_M_check(__pos, "basic_string::replace"),
			_M_limit(__pos, __n1), __n2, __c); }
		
		/**
		 *  @brief  Replace range of characters with string.
		 *  @param __i1  Iterator referencing start of range to replace.
		 *  @param __i2  Iterator referencing end of range to replace.
		 *  @param __str  String value to insert.
		 *  @return  Reference to this string.
		 *  @throw  std::length_error  If new length exceeds @c max_size().
		 *
		 *  Removes the characters in the range [__i1,__i2).  In place,
		 *  the value of @a __str is inserted.  If the length of result
		 *  exceeds max_size(), length_error is thrown.  The value of
		 *  the string doesn't change if an error is thrown.
		 */
		basic_string&
		replace(__const_iterator __i1, __const_iterator __i2,
			const basic_string& __str)
		{ return this->replace(__i1, __i2, __str._M_data(), __str.size()); }
		
		/**
		 *  @brief  Replace range of characters with C substring.
		 *  @param __i1  Iterator referencing start of range to replace.
		 *  @param __i2  Iterator referencing end of range to replace.
		 *  @param __s  C string value to insert.
		 *  @param __n  Number of characters from s to insert.
		 *  @return  Reference to this string.
		 *  @throw  std::length_error  If new length exceeds @c max_size().
		 *
		 *  Removes the characters in the range [__i1,__i2).  In place,
		 *  the first @a __n characters of @a __s are inserted.  If the
		 *  length of result exceeds max_size(), length_error is thrown.
		 *  The value of the string doesn't change if an error is
		 *  thrown.
		 */
		basic_string&
		replace(__const_iterator __i1, __const_iterator __i2,
			const _CharT* __s, size_type __n)
		{
			_GLIBCXX_DEBUG_PEDASSERT(begin() <= __i1 && __i1 <= __i2
				&& __i2 <= end());
			return this->replace(__i1 - begin(), __i2 - __i1, __s, __n);
		}
		
		/**
		 *  @brief  Replace range of characters with C string.
		 *  @param __i1  Iterator referencing start of range to replace.
		 *  @param __i2  Iterator referencing end of range to replace.
		 *  @param __s  C string value to insert.
		 *  @return  Reference to this string.
		 *  @throw  std::length_error  If new length exceeds @c max_size().
		 *
		 *  Removes the characters in the range [__i1,__i2).  In place,
		 *  the characters of @a __s are inserted.  If the length of
		 *  result exceeds max_size(), length_error is thrown.  The
		 *  value of the string doesn't change if an error is thrown.
		 */
		basic_string&
		replace(__const_iterator __i1, __const_iterator __i2, const _CharT* __s)
		{
			__glibcxx_requires_string(__s);
			return this->replace(__i1, __i2, __s, traits_type::length(__s));
		}
		
		/**
		 *  @brief  Replace range of characters with multiple characters
		 *  @param __i1  Iterator referencing start of range to replace.
		 *  @param __i2  Iterator referencing end of range to replace.
		 *  @param __n  Number of characters to insert.
		 *  @param __c  Character to insert.
		 *  @return  Reference to this string.
		 *  @throw  std::length_error  If new length exceeds @c max_size().
		 *
		 *  Removes the characters in the range [__i1,__i2).  In place,
		 *  @a __n copies of @a __c are inserted.  If the length of
		 *  result exceeds max_size(), length_error is thrown.  The
		 *  value of the string doesn't change if an error is thrown.
		 */
		basic_string&
		replace(__const_iterator __i1, __const_iterator __i2, size_type __n,
			_CharT __c)
		{
			_GLIBCXX_DEBUG_PEDASSERT(begin() <= __i1 && __i1 <= __i2
				&& __i2 <= end());
			return _M_replace_aux(__i1 - begin(), __i2 - __i1, __n, __c);
		}
		
		/**
		 *  @brief  Replace range of characters with range.
		 *  @param __i1  Iterator referencing start of range to replace.
		 *  @param __i2  Iterator referencing end of range to replace.
		 *  @param __k1  Iterator referencing start of range to insert.
		 *  @param __k2  Iterator referencing end of range to insert.
		 *  @return  Reference to this string.
		 *  @throw  std::length_error  If new length exceeds @c max_size().
		 *
		 *  Removes the characters in the range [__i1,__i2).  In place,
		 *  characters in the range [__k1,__k2) are inserted.  If the
		 *  length of result exceeds max_size(), length_error is thrown.
		 *  The value of the string doesn't change if an error is
		 *  thrown.
		 */
#if __cplusplus >= 201103L
		template<class _InputIterator,
		typename = std::_RequireInputIter<_InputIterator>>
		basic_string&
		replace(const_iterator __i1, const_iterator __i2,
			_InputIterator __k1, _InputIterator __k2)
		{
			_GLIBCXX_DEBUG_PEDASSERT(begin() <= __i1 && __i1 <= __i2
				&& __i2 <= end());
			__glibcxx_requires_valid_range(__k1, __k2);
			return this->_M_replace_dispatch(__i1, __i2, __k1, __k2,
				std::__false_type());
		}
#else
		template<class _InputIterator>
#ifdef _GLIBCXX_DISAMBIGUATE_REPLACE_INST
		typename __enable_if_not_native_iterator<_InputIterator>::__type
#else
		basic_string&
#endif
		replace(iterator __i1, iterator __i2,
			_InputIterator __k1, _InputIterator __k2)
		{
			_GLIBCXX_DEBUG_PEDASSERT(begin() <= __i1 && __i1 <= __i2
				&& __i2 <= end());
			__glibcxx_requires_valid_range(__k1, __k2);
			typedef typename std::__is_integer<_InputIterator>::__type _Integral;
			return _M_replace_dispatch(__i1, __i2, __k1, __k2, _Integral());
		}
#endif
		
		// Specializations for the common case of pointer and iterator:
		// useful to avoid the overhead of temporary buffering in _M_replace.
		basic_string&
		replace(__const_iterator __i1, __const_iterator __i2,
			_CharT* __k1, _CharT* __k2)
		{
			_GLIBCXX_DEBUG_PEDASSERT(begin() <= __i1 && __i1 <= __i2
				&& __i2 <= end());
			__glibcxx_requires_valid_range(__k1, __k2);
			return this->replace(__i1 - begin(), __i2 - __i1,
				__k1, __k2 - __k1);
		}
		
		basic_string&
		replace(__const_iterator __i1, __const_iterator __i2,
			const _CharT* __k1, const _CharT* __k2)
		{
			_GLIBCXX_DEBUG_PEDASSERT(begin() <= __i1 && __i1 <= __i2
				&& __i2 <= end());
			__glibcxx_requires_valid_range(__k1, __k2);
			return this->replace(__i1 - begin(), __i2 - __i1,
				__k1, __k2 - __k1);
		}
		
		basic_string&
		replace(__const_iterator __i1, __const_iterator __i2,
			iterator __k1, iterator __k2)
		{
			_GLIBCXX_DEBUG_PEDASSERT(begin() <= __i1 && __i1 <= __i2
				&& __i2 <= end());
			__glibcxx_requires_valid_range(__k1, __k2);
			return this->replace(__i1 - begin(), __i2 - __i1,
				__k1.base(), __k2 - __k1);
		}
		
		basic_string&
		replace(__const_iterator __i1, __const_iterator __i2,
			const_iterator __k1, const_iterator __k2)
		{
			_GLIBCXX_DEBUG_PEDASSERT(begin() <= __i1 && __i1 <= __i2
				&& __i2 <= end());
			__glibcxx_requires_valid_range(__k1, __k2);
			return this->replace(__i1 - begin(), __i2 - __i1,
				__k1.base(), __k2 - __k1);
		}
		
#if __cplusplus >= 201103L
		/**
		 *  @brief  Replace range of characters with initializer_list.
		 *  @param __i1  Iterator referencing start of range to replace.
		 *  @param __i2  Iterator referencing end of range to replace.
		 *  @param __l  The initializer_list of characters to insert.
		 *  @return  Reference to this string.
		 *  @throw  std::length_error  If new length exceeds @c max_size().
		 *
		 *  Removes the characters in the range [__i1,__i2).  In place,
		 *  characters in the range [__k1,__k2) are inserted.  If the
		 *  length of result exceeds max_size(), length_error is thrown.
		 *  The value of the string doesn't change if an error is
		 *  thrown.
		 */
		basic_string& replace(const_iterator __i1, const_iterator __i2,
			initializer_list<_CharT> __l)
		{ return this->replace(__i1, __i2, __l.begin(), __l.size()); }
#endif // C++11
		
#if __cplusplus >= 201703L
		/**
		 *  @brief  Replace range of characters with string_view.
		 *  @param __pos  The position to replace at.
		 *  @param __n    The number of characters to replace.
		 *  @param __svt  The object convertible to string_view to insert.
		 *  @return  Reference to this string.
		 */
		template<typename _Tp>
		_If_sv<_Tp, basic_string&>
		replace(size_type __pos, size_type __n, const _Tp& __svt)
		{
			__sv_type __sv = __svt;
			return this->replace(__pos, __n, __sv.data(), __sv.size());
		}
		
		/**
		 *  @brief  Replace range of characters with string_view.
		 *  @param __pos1  The position to replace at.
		 *  @param __n1    The number of characters to replace.
		 *  @param __svt   The object convertible to string_view to insert from.
		 *  @param __pos2  The position in the string_view to insert from.
		 *  @param __n2    The number of characters to insert.
		 *  @return  Reference to this string.
		 */
		template<typename _Tp>
		_If_sv<_Tp, basic_string&>
		replace(size_type __pos1, size_type __n1, const _Tp& __svt,
			size_type __pos2, size_type __n2 = npos)
		{
			__sv_type __sv = __svt;
			return this->replace(__pos1, __n1,
				__sv.data()
				+ std::__sv_check(__sv.size(), __pos2, "basic_string::replace"),
				std::__sv_limit(__sv.size(), __pos2, __n2));
		}
		
		/**
		 *  @brief  Replace range of characters with string_view.
		 *  @param __i1    An iterator referencing the start position
		  to replace at.
		 *  @param __i2    An iterator referencing the end position
		  for the replace.
		 *  @param __svt   The object convertible to string_view to insert from.
		 *  @return  Reference to this string.
		 */
		template<typename _Tp>
		_If_sv<_Tp, basic_string&>
		replace(const_iterator __i1, const_iterator __i2, const _Tp& __svt)
		{
			__sv_type __sv = __svt;
			return this->replace(__i1 - begin(), __i2 - __i1, __sv);
		}
#endif // C++17
		
	private:
		template<class _Integer>
		basic_string&
		_M_replace_dispatch(const_iterator __i1, const_iterator __i2,
			_Integer __n, _Integer __val, __true_type)
		{ return _M_replace_aux(__i1 - begin(), __i2 - __i1, __n, __val); }
		
		template<class _InputIterator>
		basic_string&
		_M_replace_dispatch(const_iterator __i1, const_iterator __i2,
			_InputIterator __k1, _InputIterator __k2,
			__false_type);
		
		basic_string&
		_M_replace_aux(size_type __pos1, size_type __n1, size_type __n2,
			_CharT __c);
		
		basic_string&
		_M_replace(size_type __pos, size_type __len1, const _CharT* __s,
			const size_type __len2);
		
		basic_string&
		_M_append(const _CharT* __s, size_type __n);
		
	public:
		
		/**
		 *  @brief  Copy substring into C string.
		 *  @param __s  C string to copy value into.
		 *  @param __n  Number of characters to copy.
		 *  @param __pos  Index of first character to copy.
		 *  @return  Number of characters actually copied
		 *  @throw  std::out_of_range  If __pos > size().
		 *
		 *  Copies up to @a __n characters starting at @a __pos into the
		 *  C string @a __s.  If @a __pos is %greater than size(),
		 *  out_of_range is thrown.
		 */
		size_type
		copy(_CharT* __s, size_type __n, size_type __pos = 0) const;
		
		/**
		 *  @brief  Swap contents with another string.
		 *  @param __s  String to swap with.
		 *
		 *  Exchanges the contents of this string with that of @a __s in constant
		 *  time.
		 */
		void
		swap(basic_string& __s) _GLIBCXX_NOEXCEPT;
		
		// String operations:
		/**
		 *  @brief  Return const pointer to null-terminated contents.
		 *
		 *  This is a handle to internal data.  Do not modify or dire things may
		 *  happen.
		 */
		const _CharT*
		c_str() const _GLIBCXX_NOEXCEPT
		{ return _M_data(); }
		
		/**
		 *  @brief  Return const pointer to contents.
		 *
		 *  This is a pointer to internal data.  It is undefined to modify
		 *  the contents through the returned pointer. To get a pointer that
		 *  allows modifying the contents use @c &str[0] instead,
		 *  (or in C++17 the non-const @c str.data() overload).
		 */
		const _CharT*
		data() const _GLIBCXX_NOEXCEPT
		{ return _M_data(); }
		
#if __cplusplus >= 201703L
		/**
		 *  @brief  Return non-const pointer to contents.
		 *
		 *  This is a pointer to the character sequence held by the string.
		 *  Modifying the characters in the sequence is allowed.
		 */
		_CharT*
		data() noexcept
		{ return _M_data(); }
#endif
		
		/**
		 *  @brief  Return copy of allocator used to construct this string.
		 */
		allocator_type
		get_allocator() const _GLIBCXX_NOEXCEPT
		{ return _M_get_allocator(); }
		
		/**
		 *  @brief  Find position of a C substring.
		 *  @param __s  C string to locate.
		 *  @param __pos  Index of character to search from.
		 *  @param __n  Number of characters from @a s to search for.
		 *  @return  Index of start of first occurrence.
		 *
		 *  Starting from @a __pos, searches forward for the first @a
		 *  __n characters in @a __s within this string.  If found,
		 *  returns the index where it begins.  If not found, returns
		 *  npos.
		 */
		size_type
		find(const _CharT* __s, size_type __pos, size_type __n) const
		_GLIBCXX_NOEXCEPT;
		
		/**
		 *  @brief  Find position of a string.
		 *  @param __str  String to locate.
		 *  @param __pos  Index of character to search from (default 0).
		 *  @return  Index of start of first occurrence.
		 *
		 *  Starting from @a __pos, searches forward for value of @a __str within
		 *  this string.  If found, returns the index where it begins.  If not
		 *  found, returns npos.
		 */
		size_type
		find(const basic_string& __str, size_type __pos = 0) const
		_GLIBCXX_NOEXCEPT
		{ return this->find(__str.data(), __pos, __str.size()); }
		
#if __cplusplus >= 201703L
		/**
		 *  @brief  Find position of a string_view.
		 *  @param __svt  The object convertible to string_view to locate.
		 *  @param __pos  Index of character to search from (default 0).
		 *  @return  Index of start of first occurrence.
		 */
		template<typename _Tp>
		_If_sv<_Tp, size_type>
		find(const _Tp& __svt, size_type __pos = 0) const
		noexcept(is_same<_Tp, __sv_type>::value)
		{
			__sv_type __sv = __svt;
			return this->find(__sv.data(), __pos, __sv.size());
		}
#endif // C++17
		
		/**
		 *  @brief  Find position of a C string.
		 *  @param __s  C string to locate.
		 *  @param __pos  Index of character to search from (default 0).
		 *  @return  Index of start of first occurrence.
		 *
		 *  Starting from @a __pos, searches forward for the value of @a
		 *  __s within this string.  If found, returns the index where
		 *  it begins.  If not found, returns npos.
		 */
		size_type
		find(const _CharT* __s, size_type __pos = 0) const _GLIBCXX_NOEXCEPT
		{
			__glibcxx_requires_string(__s);
			return this->find(__s, __pos, traits_type::length(__s));
		}
		
		/**
		 *  @brief  Find position of a character.
		 *  @param __c  Character to locate.
		 *  @param __pos  Index of character to search from (default 0).
		 *  @return  Index of first occurrence.
		 *
		 *  Starting from @a __pos, searches forward for @a __c within
		 *  this string.  If found, returns the index where it was
		 *  found.  If not found, returns npos.
		 */
		size_type
		find(_CharT __c, size_type __pos = 0) const _GLIBCXX_NOEXCEPT;
		
		/**
		 *  @brief  Find last position of a string.
		 *  @param __str  String to locate.
		 *  @param __pos  Index of character to search back from (default end).
		 *  @return  Index of start of last occurrence.
		 *
		 *  Starting from @a __pos, searches backward for value of @a
		 *  __str within this string.  If found, returns the index where
		 *  it begins.  If not found, returns npos.
		 */
		size_type
		rfind(const basic_string& __str, size_type __pos = npos) const
		_GLIBCXX_NOEXCEPT
		{ return this->rfind(__str.data(), __pos, __str.size()); }
		
#if __cplusplus >= 201703L
		/**
		 *  @brief  Find last position of a string_view.
		 *  @param __svt  The object convertible to string_view to locate.
		 *  @param __pos  Index of character to search back from (default end).
		 *  @return  Index of start of last occurrence.
		 */
		template<typename _Tp>
		_If_sv<_Tp, size_type>
		rfind(const _Tp& __svt, size_type __pos = npos) const
		noexcept(is_same<_Tp, __sv_type>::value)
		{
			__sv_type __sv = __svt;
			return this->rfind(__sv.data(), __pos, __sv.size());
		}
#endif // C++17
		
		/**
		 *  @brief  Find last position of a C substring.
		 *  @param __s  C string to locate.
		 *  @param __pos  Index of character to search back from.
		 *  @param __n  Number of characters from s to search for.
		 *  @return  Index of start of last occurrence.
		 *
		 *  Starting from @a __pos, searches backward for the first @a
		 *  __n characters in @a __s within this string.  If found,
		 *  returns the index where it begins.  If not found, returns
		 *  npos.
		 */
		size_type
		rfind(const _CharT* __s, size_type __pos, size_type __n) const
		_GLIBCXX_NOEXCEPT;
		
		/**
		 *  @brief  Find last position of a C string.
		 *  @param __s  C string to locate.
		 *  @param __pos  Index of character to start search at (default end).
		 *  @return  Index of start of  last occurrence.
		 *
		 *  Starting from @a __pos, searches backward for the value of
		 *  @a __s within this string.  If found, returns the index
		 *  where it begins.  If not found, returns npos.
		 */
		size_type
		rfind(const _CharT* __s, size_type __pos = npos) const
		{
			__glibcxx_requires_string(__s);
			return this->rfind(__s, __pos, traits_type::length(__s));
		}
		
		/**
		 *  @brief  Find last position of a character.
		 *  @param __c  Character to locate.
		 *  @param __pos  Index of character to search back from (default end).
		 *  @return  Index of last occurrence.
		 *
		 *  Starting from @a __pos, searches backward for @a __c within
		 *  this string.  If found, returns the index where it was
		 *  found.  If not found, returns npos.
		 */
		size_type
		rfind(_CharT __c, size_type __pos = npos) const _GLIBCXX_NOEXCEPT;
		
		/**
		 *  @brief  Find position of a character of string.
		 *  @param __str  String containing characters to locate.
		 *  @param __pos  Index of character to search from (default 0).
		 *  @return  Index of first occurrence.
		 *
		 *  Starting from @a __pos, searches forward for one of the
		 *  characters of @a __str within this string.  If found,
		 *  returns the index where it was found.  If not found, returns
		 *  npos.
		 */
		size_type
		find_first_of(const basic_string& __str, size_type __pos = 0) const
		_GLIBCXX_NOEXCEPT
		{ return this->find_first_of(__str.data(), __pos, __str.size()); }
		
#if __cplusplus >= 201703L
		/**
		 *  @brief  Find position of a character of a string_view.
		 *  @param __svt  An object convertible to string_view containing
		 *                characters to locate.
		 *  @param __pos  Index of character to search from (default 0).
		 *  @return  Index of first occurrence.
		 */
		template<typename _Tp>
		_If_sv<_Tp, size_type>
		find_first_of(const _Tp& __svt, size_type __pos = 0) const
		noexcept(is_same<_Tp, __sv_type>::value)
		{
			__sv_type __sv = __svt;
			return this->find_first_of(__sv.data(), __pos, __sv.size());
		}
#endif // C++17
		
		/**
		 *  @brief  Find position of a character of C substring.
		 *  @param __s  String containing characters to locate.
		 *  @param __pos  Index of character to search from.
		 *  @param __n  Number of characters from s to search for.
		 *  @return  Index of first occurrence.
		 *
		 *  Starting from @a __pos, searches forward for one of the
		 *  first @a __n characters of @a __s within this string.  If
		 *  found, returns the index where it was found.  If not found,
		 *  returns npos.
		 */
		size_type
		find_first_of(const _CharT* __s, size_type __pos, size_type __n) const
		_GLIBCXX_NOEXCEPT;
		
		/**
		 *  @brief  Find position of a character of C string.
		 *  @param __s  String containing characters to locate.
		 *  @param __pos  Index of character to search from (default 0).
		 *  @return  Index of first occurrence.
		 *
		 *  Starting from @a __pos, searches forward for one of the
		 *  characters of @a __s within this string.  If found, returns
		 *  the index where it was found.  If not found, returns npos.
		 */
		size_type
		find_first_of(const _CharT* __s, size_type __pos = 0) const
		_GLIBCXX_NOEXCEPT
		{
			__glibcxx_requires_string(__s);
			return this->find_first_of(__s, __pos, traits_type::length(__s));
		}
		
		/**
		 *  @brief  Find position of a character.
		 *  @param __c  Character to locate.
		 *  @param __pos  Index of character to search from (default 0).
		 *  @return  Index of first occurrence.
		 *
		 *  Starting from @a __pos, searches forward for the character
		 *  @a __c within this string.  If found, returns the index
		 *  where it was found.  If not found, returns npos.
		 *
		 *  Note: equivalent to find(__c, __pos).
		 */
		size_type
		find_first_of(_CharT __c, size_type __pos = 0) const _GLIBCXX_NOEXCEPT
		{ return this->find(__c, __pos); }
		
		/**
		 *  @brief  Find last position of a character of string.
		 *  @param __str  String containing characters to locate.
		 *  @param __pos  Index of character to search back from (default end).
		 *  @return  Index of last occurrence.
		 *
		 *  Starting from @a __pos, searches backward for one of the
		 *  characters of @a __str within this string.  If found,
		 *  returns the index where it was found.  If not found, returns
		 *  npos.
		 */
		size_type
		find_last_of(const basic_string& __str, size_type __pos = npos) const
		_GLIBCXX_NOEXCEPT
		{ return this->find_last_of(__str.data(), __pos, __str.size()); }
		
#if __cplusplus >= 201703L
		/**
		 *  @brief  Find last position of a character of string.
		 *  @param __svt  An object convertible to string_view containing
		 *                characters to locate.
		 *  @param __pos  Index of character to search back from (default end).
		 *  @return  Index of last occurrence.
		 */
		template<typename _Tp>
		_If_sv<_Tp, size_type>
		find_last_of(const _Tp& __svt, size_type __pos = npos) const
		noexcept(is_same<_Tp, __sv_type>::value)
		{
			__sv_type __sv = __svt;
			return this->find_last_of(__sv.data(), __pos, __sv.size());
		}
#endif // C++17
		
		/**
		 *  @brief  Find last position of a character of C substring.
		 *  @param __s  C string containing characters to locate.
		 *  @param __pos  Index of character to search back from.
		 *  @param __n  Number of characters from s to search for.
		 *  @return  Index of last occurrence.
		 *
		 *  Starting from @a __pos, searches backward for one of the
		 *  first @a __n characters of @a __s within this string.  If
		 *  found, returns the index where it was found.  If not found,
		 *  returns npos.
		 */
		size_type
		find_last_of(const _CharT* __s, size_type __pos, size_type __n) const
		_GLIBCXX_NOEXCEPT;
		
		/**
		 *  @brief  Find last position of a character of C string.
		 *  @param __s  C string containing characters to locate.
		 *  @param __pos  Index of character to search back from (default end).
		 *  @return  Index of last occurrence.
		 *
		 *  Starting from @a __pos, searches backward for one of the
		 *  characters of @a __s within this string.  If found, returns
		 *  the index where it was found.  If not found, returns npos.
		 */
		size_type
		find_last_of(const _CharT* __s, size_type __pos = npos) const
		_GLIBCXX_NOEXCEPT
		{
			__glibcxx_requires_string(__s);
			return this->find_last_of(__s, __pos, traits_type::length(__s));
		}
		
		/**
		 *  @brief  Find last position of a character.
		 *  @param __c  Character to locate.
		 *  @param __pos  Index of character to search back from (default end).
		 *  @return  Index of last occurrence.
		 *
		 *  Starting from @a __pos, searches backward for @a __c within
		 *  this string.  If found, returns the index where it was
		 *  found.  If not found, returns npos.
		 *
		 *  Note: equivalent to rfind(__c, __pos).
		 */
		size_type
		find_last_of(_CharT __c, size_type __pos = npos) const _GLIBCXX_NOEXCEPT
		{ return this->rfind(__c, __pos); }
		
		/**
		 *  @brief  Find position of a character not in string.
		 *  @param __str  String containing characters to avoid.
		 *  @param __pos  Index of character to search from (default 0).
		 *  @return  Index of first occurrence.
		 *
		 *  Starting from @a __pos, searches forward for a character not contained
		 *  in @a __str within this string.  If found, returns the index where it
		 *  was found.  If not found, returns npos.
		 */
		size_type
		find_first_not_of(const basic_string& __str, size_type __pos = 0) const
		_GLIBCXX_NOEXCEPT
		{ return this->find_first_not_of(__str.data(), __pos, __str.size()); }
		
#if __cplusplus >= 201703L
		/**
		 *  @brief  Find position of a character not in a string_view.
		 *  @param __svt  A object convertible to string_view containing
		 *                characters to avoid.
		 *  @param __pos  Index of character to search from (default 0).
		 *  @return  Index of first occurrence.
		 */
		template<typename _Tp>
		_If_sv<_Tp, size_type>
		find_first_not_of(const _Tp& __svt, size_type __pos = 0) const
		noexcept(is_same<_Tp, __sv_type>::value)
		{
			__sv_type __sv = __svt;
			return this->find_first_not_of(__sv.data(), __pos, __sv.size());
		}
#endif // C++17
		
		/**
		 *  @brief  Find position of a character not in C substring.
		 *  @param __s  C string containing characters to avoid.
		 *  @param __pos  Index of character to search from.
		 *  @param __n  Number of characters from __s to consider.
		 *  @return  Index of first occurrence.
		 *
		 *  Starting from @a __pos, searches forward for a character not
		 *  contained in the first @a __n characters of @a __s within
		 *  this string.  If found, returns the index where it was
		 *  found.  If not found, returns npos.
		 */
		size_type
		find_first_not_of(const _CharT* __s, size_type __pos,
			size_type __n) const _GLIBCXX_NOEXCEPT;
		
		/**
		 *  @brief  Find position of a character not in C string.
		 *  @param __s  C string containing characters to avoid.
		 *  @param __pos  Index of character to search from (default 0).
		 *  @return  Index of first occurrence.
		 *
		 *  Starting from @a __pos, searches forward for a character not
		 *  contained in @a __s within this string.  If found, returns
		 *  the index where it was found.  If not found, returns npos.
		 */
		size_type
		find_first_not_of(const _CharT* __s, size_type __pos = 0) const
		_GLIBCXX_NOEXCEPT
		{
			__glibcxx_requires_string(__s);
			return this->find_first_not_of(__s, __pos, traits_type::length(__s));
		}
		
		/**
		 *  @brief  Find position of a different character.
		 *  @param __c  Character to avoid.
		 *  @param __pos  Index of character to search from (default 0).
		 *  @return  Index of first occurrence.
		 *
		 *  Starting from @a __pos, searches forward for a character
		 *  other than @a __c within this string.  If found, returns the
		 *  index where it was found.  If not found, returns npos.
		 */
		size_type
		find_first_not_of(_CharT __c, size_type __pos = 0) const
		_GLIBCXX_NOEXCEPT;
		
		/**
		 *  @brief  Find last position of a character not in string.
		 *  @param __str  String containing characters to avoid.
		 *  @param __pos  Index of character to search back from (default end).
		 *  @return  Index of last occurrence.
		 *
		 *  Starting from @a __pos, searches backward for a character
		 *  not contained in @a __str within this string.  If found,
		 *  returns the index where it was found.  If not found, returns
		 *  npos.
		 */
		size_type
		find_last_not_of(const basic_string& __str, size_type __pos = npos) const
		_GLIBCXX_NOEXCEPT
		{ return this->find_last_not_of(__str.data(), __pos, __str.size()); }
		
#if __cplusplus >= 201703L
		/**
		 *  @brief  Find last position of a character not in a string_view.
		 *  @param __svt  An object convertible to string_view containing
		 *                characters to avoid.
		 *  @param __pos  Index of character to search back from (default end).
		 *  @return  Index of last occurrence.
		 */
		template<typename _Tp>
		_If_sv<_Tp, size_type>
		find_last_not_of(const _Tp& __svt, size_type __pos = npos) const
		noexcept(is_same<_Tp, __sv_type>::value)
		{
			__sv_type __sv = __svt;
			return this->find_last_not_of(__sv.data(), __pos, __sv.size());
		}
#endif // C++17
		
		/**
		 *  @brief  Find last position of a character not in C substring.
		 *  @param __s  C string containing characters to avoid.
		 *  @param __pos  Index of character to search back from.
		 *  @param __n  Number of characters from s to consider.
		 *  @return  Index of last occurrence.
		 *
		 *  Starting from @a __pos, searches backward for a character not
		 *  contained in the first @a __n characters of @a __s within this string.
		 *  If found, returns the index where it was found.  If not found,
		 *  returns npos.
		 */
		size_type
		find_last_not_of(const _CharT* __s, size_type __pos,
			size_type __n) const _GLIBCXX_NOEXCEPT;
		/**
		 *  @brief  Find last position of a character not in C string.
		 *  @param __s  C string containing characters to avoid.
		 *  @param __pos  Index of character to search back from (default end).
		 *  @return  Index of last occurrence.
		 *
		 *  Starting from @a __pos, searches backward for a character
		 *  not contained in @a __s within this string.  If found,
		 *  returns the index where it was found.  If not found, returns
		 *  npos.
		 */
		size_type
		find_last_not_of(const _CharT* __s, size_type __pos = npos) const
		_GLIBCXX_NOEXCEPT
		{
			__glibcxx_requires_string(__s);
			return this->find_last_not_of(__s, __pos, traits_type::length(__s));
		}
		
		/**
		 *  @brief  Find last position of a different character.
		 *  @param __c  Character to avoid.
		 *  @param __pos  Index of character to search back from (default end).
		 *  @return  Index of last occurrence.
		 *
		 *  Starting from @a __pos, searches backward for a character other than
		 *  @a __c within this string.  If found, returns the index where it was
		 *  found.  If not found, returns npos.
		 */
		size_type
		find_last_not_of(_CharT __c, size_type __pos = npos) const
		_GLIBCXX_NOEXCEPT;
		
		/**
		 *  @brief  Get a substring.
		 *  @param __pos  Index of first character (default 0).
		 *  @param __n  Number of characters in substring (default remainder).
		 *  @return  The new string.
		 *  @throw  std::out_of_range  If __pos > size().
		 *
		 *  Construct and return a new string using the @a __n
		 *  characters starting at @a __pos.  If the string is too
		 *  short, use the remainder of the characters.  If @a __pos is
		 *  beyond the end of the string, out_of_range is thrown.
		 */
		basic_string
		substr(size_type __pos = 0, size_type __n = npos) const
		{ return basic_string(*this,
			_M_check(__pos, "basic_string::substr"), __n); }
		
		/**
		 *  @brief  Compare to a string.
		 *  @param __str  String to compare against.
		 *  @return  Integer < 0, 0, or > 0.
		 *
		 *  Returns an integer < 0 if this string is ordered before @a
		 *  __str, 0 if their values are equivalent, or > 0 if this
		 *  string is ordered after @a __str.  Determines the effective
		 *  length rlen of the strings to compare as the smallest of
		 *  size() and str.size().  The function then compares the two
		 *  strings by calling traits::compare(data(), str.data(),rlen).
		 *  If the result of the comparison is nonzero returns it,
		 *  otherwise the shorter one is ordered first.
		 */
		int
		compare(const basic_string& __str) const
		{
			const size_type __size = this->size();
			const size_type __osize = __str.size();
			const size_type __len = std::min(__size, __osize);
			
			int __r = traits_type::compare(_M_data(), __str.data(), __len);
			if (!__r)
				__r = _S_compare(__size, __osize);
			return __r;
		}
		
#if __cplusplus >= 201703L
		/**
		 *  @brief  Compare to a string_view.
		 *  @param __svt An object convertible to string_view to compare against.
		 *  @return  Integer < 0, 0, or > 0.
		 */
		template<typename _Tp>
		_If_sv<_Tp, int>
		compare(const _Tp& __svt) const
		noexcept(is_same<_Tp, __sv_type>::value)
		{
			__sv_type __sv = __svt;
			const size_type __size = this->size();
			const size_type __osize = __sv.size();
			const size_type __len = std::min(__size, __osize);
			
			int __r = traits_type::compare(_M_data(), __sv.data(), __len);
			if (!__r)
				__r = _S_compare(__size, __osize);
			return __r;
		}
		
		/**
		 *  @brief  Compare to a string_view.
		 *  @param __pos  A position in the string to start comparing from.
		 *  @param __n  The number of characters to compare.
		 *  @param __svt  An object convertible to string_view to compare
		 *                against.
		 *  @return  Integer < 0, 0, or > 0.
		 */
		template<typename _Tp>
		_If_sv<_Tp, int>
		compare(size_type __pos, size_type __n, const _Tp& __svt) const
		noexcept(is_same<_Tp, __sv_type>::value)
		{
			__sv_type __sv = __svt;
			return __sv_type(*this).substr(__pos, __n).compare(__sv);
		}
		
		/**
		 *  @brief  Compare to a string_view.
		 *  @param __pos1  A position in the string to start comparing from.
		 *  @param __n1  The number of characters to compare.
		 *  @param __svt  An object convertible to string_view to compare
		 *                against.
		 *  @param __pos2  A position in the string_view to start comparing from.
		 *  @param __n2  The number of characters to compare.
		 *  @return  Integer < 0, 0, or > 0.
		 */
		template<typename _Tp>
		_If_sv<_Tp, int>
		compare(size_type __pos1, size_type __n1, const _Tp& __svt,
			size_type __pos2, size_type __n2 = npos) const
		noexcept(is_same<_Tp, __sv_type>::value)
		{
			__sv_type __sv = __svt;
			return __sv_type(*this)
			.substr(__pos1, __n1).compare(__sv.substr(__pos2, __n2));
		}
#endif // C++17
		
		/**
		 *  @brief  Compare substring to a string.
		 *  @param __pos  Index of first character of substring.
		 *  @param __n  Number of characters in substring.
		 *  @param __str  String to compare against.
		 *  @return  Integer < 0, 0, or > 0.
		 *
		 *  Form the substring of this string from the @a __n characters
		 *  starting at @a __pos.  Returns an integer < 0 if the
		 *  substring is ordered before @a __str, 0 if their values are
		 *  equivalent, or > 0 if the substring is ordered after @a
		 *  __str.  Determines the effective length rlen of the strings
		 *  to compare as the smallest of the length of the substring
		 *  and @a __str.size().  The function then compares the two
		 *  strings by calling
		 *  traits::compare(substring.data(),str.data(),rlen).  If the
		 *  result of the comparison is nonzero returns it, otherwise
		 *  the shorter one is ordered first.
		 */
		int
		compare(size_type __pos, size_type __n, const basic_string& __str) const;
		
		/**
		 *  @brief  Compare substring to a substring.
		 *  @param __pos1  Index of first character of substring.
		 *  @param __n1  Number of characters in substring.
		 *  @param __str  String to compare against.
		 *  @param __pos2  Index of first character of substring of str.
		 *  @param __n2  Number of characters in substring of str.
		 *  @return  Integer < 0, 0, or > 0.
		 *
		 *  Form the substring of this string from the @a __n1
		 *  characters starting at @a __pos1.  Form the substring of @a
		 *  __str from the @a __n2 characters starting at @a __pos2.
		 *  Returns an integer < 0 if this substring is ordered before
		 *  the substring of @a __str, 0 if their values are equivalent,
		 *  or > 0 if this substring is ordered after the substring of
		 *  @a __str.  Determines the effective length rlen of the
		 *  strings to compare as the smallest of the lengths of the
		 *  substrings.  The function then compares the two strings by
		 *  calling
		 *  traits::compare(substring.data(),str.substr(pos2,n2).data(),rlen).
		 *  If the result of the comparison is nonzero returns it,
		 *  otherwise the shorter one is ordered first.
		 */
		int
		compare(size_type __pos1, size_type __n1, const basic_string& __str,
			size_type __pos2, size_type __n2 = npos) const;
		
		/**
		 *  @brief  Compare to a C string.
		 *  @param __s  C string to compare against.
		 *  @return  Integer < 0, 0, or > 0.
		 *
		 *  Returns an integer < 0 if this string is ordered before @a __s, 0 if
		 *  their values are equivalent, or > 0 if this string is ordered after
		 *  @a __s.  Determines the effective length rlen of the strings to
		 *  compare as the smallest of size() and the length of a string
		 *  constructed from @a __s.  The function then compares the two strings
		 *  by calling traits::compare(data(),s,rlen).  If the result of the
		 *  comparison is nonzero returns it, otherwise the shorter one is
		 *  ordered first.
		 */
		int
		compare(const _CharT* __s) const _GLIBCXX_NOEXCEPT;
		
		// _GLIBCXX_RESOLVE_LIB_DEFECTS
		// 5 String::compare specification questionable
		/**
		 *  @brief  Compare substring to a C string.
		 *  @param __pos  Index of first character of substring.
		 *  @param __n1  Number of characters in substring.
		 *  @param __s  C string to compare against.
		 *  @return  Integer < 0, 0, or > 0.
		 *
		 *  Form the substring of this string from the @a __n1
		 *  characters starting at @a pos.  Returns an integer < 0 if
		 *  the substring is ordered before @a __s, 0 if their values
		 *  are equivalent, or > 0 if the substring is ordered after @a
		 *  __s.  Determines the effective length rlen of the strings to
		 *  compare as the smallest of the length of the substring and
		 *  the length of a string constructed from @a __s.  The
		 *  function then compares the two string by calling
		 *  traits::compare(substring.data(),__s,rlen).  If the result of
		 *  the comparison is nonzero returns it, otherwise the shorter
		 *  one is ordered first.
		 */
		int
		compare(size_type __pos, size_type __n1, const _CharT* __s) const;
		
		/**
		 *  @brief  Compare substring against a character %array.
		 *  @param __pos  Index of first character of substring.
		 *  @param __n1  Number of characters in substring.
		 *  @param __s  character %array to compare against.
		 *  @param __n2  Number of characters of s.
		 *  @return  Integer < 0, 0, or > 0.
		 *
		 *  Form the substring of this string from the @a __n1
		 *  characters starting at @a __pos.  Form a string from the
		 *  first @a __n2 characters of @a __s.  Returns an integer < 0
		 *  if this substring is ordered before the string from @a __s,
		 *  0 if their values are equivalent, or > 0 if this substring
		 *  is ordered after the string from @a __s.  Determines the
		 *  effective length rlen of the strings to compare as the
		 *  smallest of the length of the substring and @a __n2.  The
		 *  function then compares the two strings by calling
		 *  traits::compare(substring.data(),s,rlen).  If the result of
		 *  the comparison is nonzero returns it, otherwise the shorter
		 *  one is ordered first.
		 *
		 *  NB: s must have at least n2 characters, &apos;\\0&apos; has
		 *  no special meaning.
		 */
		int
		compare(size_type __pos, size_type __n1, const _CharT* __s,
			size_type __n2) const;
		
#if __cplusplus > 201703L
		bool
		starts_with(basic_string_view<_CharT, _Traits> __x) const noexcept
		{ return __sv_type(this->data(), this->size()).starts_with(__x); }
		
		bool
		starts_with(_CharT __x) const noexcept
		{ return __sv_type(this->data(), this->size()).starts_with(__x); }
		
		bool
		starts_with(const _CharT* __x) const noexcept
		{ return __sv_type(this->data(), this->size()).starts_with(__x); }
		
		bool
		ends_with(basic_string_view<_CharT, _Traits> __x) const noexcept
		{ return __sv_type(this->data(), this->size()).ends_with(__x); }
		
		bool
		ends_with(_CharT __x) const noexcept
		{ return __sv_type(this->data(), this->size()).ends_with(__x); }
		
		bool
		ends_with(const _CharT* __x) const noexcept
		{ return __sv_type(this->data(), this->size()).ends_with(__x); }
#endif // C++20
		
#if __cplusplus > 202002L
		bool
		contains(basic_string_view<_CharT, _Traits> __x) const noexcept
		{ return __sv_type(this->data(), this->size()).contains(__x); }
		
		bool
		contains(_CharT __x) const noexcept
		{ return __sv_type(this->data(), this->size()).contains(__x); }
		
		bool
		contains(const _CharT* __x) const noexcept
		{ return __sv_type(this->data(), this->size()).contains(__x); }
#endif // C++23
		
		// Allow basic_stringbuf::__xfer_bufptrs to call _M_length:
		template<typename, typename, typename> friend class basic_stringbuf;
	};
	_GLIBCXX_END_NAMESPACE_CXX11
#else  // !_GLIBCXX_USE_CXX11_ABI
	// Reference-counted COW string implentation
	
	/**
	 *  @class basic_string basic_string.h <string>
	 *  @brief  Managing sequences of characters and character-like objects.
	 *
	 *  @ingroup strings
	 *  @ingroup sequences
	 *
	 *  @tparam _CharT  Type of character
	 *  @tparam _Traits  Traits for character type, defaults to
	 *                   char_traits<_CharT>.
	 *  @tparam _Alloc  Allocator type, defaults to allocator<_CharT>.
	 *
	 *  Meets the requirements of a <a href="tables.html#65">container</a>, a
	 *  <a href="tables.html#66">reversible container</a>, and a
	 *  <a href="tables.html#67">sequence</a>.  Of the
	 *  <a href="tables.html#68">optional sequence requirements</a>, only
	 *  @c push_back, @c at, and @c %array access are supported.
	 *
	 *  @doctodo
	 *
	 *
	 *  Documentation?  What's that?
	 *  Nathan Myers <ncm@cantrip.org>.
	 *
	 *  A string looks like this:
	 *
	 *  @code
	 *                                        [_Rep]
	 *                                        _M_length
	 *   [basic_string<char_type>]            _M_capacity
	 *   _M_dataplus                          _M_refcount
	 *   _M_p ---------------->               unnamed array of char_type
	 *  @endcode
	 *
	 *  Where the _M_p points to the first character in the string, and
	 *  you cast it to a pointer-to-_Rep and subtract 1 to get a
	 *  pointer to the header.
	 *
	 *  This approach has the enormous advantage that a string object
	 *  requires only one allocation.  All the ugliness is confined
	 *  within a single %pair of inline functions, which each compile to
	 *  a single @a add instruction: _Rep::_M_data(), and
	 *  string::_M_rep(); and the allocation function which gets a
	 *  block of raw bytes and with room enough and constructs a _Rep
	 *  object at the front.
	 *
	 *  The reason you want _M_data pointing to the character %array and
	 *  not the _Rep is so that the debugger can see the string
	 *  contents. (Probably we should add a non-inline member to get
	 *  the _Rep for the debugger to use, so users can check the actual
	 *  string length.)
	 *
	 *  Note that the _Rep object is a POD so that you can have a
	 *  static <em>empty string</em> _Rep object already @a constructed before
	 *  static constructors have run.  The reference-count encoding is
	 *  chosen so that a 0 indicates one reference, so you never try to
	 *  destroy the empty-string _Rep object.
	 *
	 *  All but the last paragraph is considered pretty conventional
	 *  for a C++ string implementation.
	 */
	// 21.3  Template class basic_string
	template<typename _CharT, typename _Traits, typename _Alloc>
	class basic_string
	{
		typedef typename __gnu_cxx::__alloc_traits<_Alloc>::template
		rebind<_CharT>::other _CharT_alloc_type;
		typedef __gnu_cxx::__alloc_traits<_CharT_alloc_type> _CharT_alloc_traits;
		
		// Types:
	public:
		typedef _Traits					    traits_type;
		typedef typename _Traits::char_type		    value_type;
		typedef _Alloc					    allocator_type;
		typedef typename _CharT_alloc_traits::size_type	    size_type;
		typedef typename _CharT_alloc_traits::difference_type difference_type;
#if __cplusplus < 201103L
		typedef typename _CharT_alloc_type::reference	    reference;
		typedef typename _CharT_alloc_type::const_reference   const_reference;
#else
		typedef value_type&				    reference;
		typedef const value_type&				    const_reference;
#endif
		typedef typename _CharT_alloc_traits::pointer	    pointer;
		typedef typename _CharT_alloc_traits::const_pointer   const_pointer;
		typedef __gnu_cxx::__normal_iterator<pointer, basic_string>  iterator;
		typedef __gnu_cxx::__normal_iterator<const_pointer, basic_string>
		const_iterator;
		typedef std::reverse_iterator<const_iterator>	const_reverse_iterator;
		typedef std::reverse_iterator<iterator>		    reverse_iterator;
		
	protected:
		// type used for positions in insert, erase etc.
		typedef iterator __const_iterator;
		
	private:
		// _Rep: string representation
		//   Invariants:
		//   1. String really contains _M_length + 1 characters: due to 21.3.4
		//      must be kept null-terminated.
		//   2. _M_capacity >= _M_length
		//      Allocated memory is always (_M_capacity + 1) * sizeof(_CharT).
		//   3. _M_refcount has three states:
		//      -1: leaked, one reference, no ref-copies allowed, non-const.
		//       0: one reference, non-const.
		//     n>0: n + 1 references, operations require a lock, const.
		//   4. All fields==0 is an empty string, given the extra storage
		//      beyond-the-end for a null terminator; thus, the shared
		//      empty string representation needs no constructor.
		
		struct _Rep_base
		{
			size_type		_M_length;
			size_type		_M_capacity;
			_Atomic_word		_M_refcount;
		};
		
		struct _Rep : _Rep_base
		{
			// Types:
			typedef typename __gnu_cxx::__alloc_traits<_Alloc>::template
			rebind<char>::other _Raw_bytes_alloc;
			
			// (Public) Data members:
			
			// The maximum number of individual char_type elements of an
			// individual string is determined by _S_max_size. This is the
			// value that will be returned by max_size().  (Whereas npos
			// is the maximum number of bytes the allocator can allocate.)
			// If one was to divvy up the theoretical largest size string,
			// with a terminating character and m _CharT elements, it'd
			// look like this:
			// npos = sizeof(_Rep) + (m * sizeof(_CharT)) + sizeof(_CharT)
			// Solving for m:
			// m = ((npos - sizeof(_Rep))/sizeof(CharT)) - 1
			// In addition, this implementation quarters this amount.
			static const size_type	_S_max_size;
			static const _CharT	_S_terminal;
			
			// The following storage is init'd to 0 by the linker, resulting
			// (carefully) in an empty string with one reference.
			static size_type _S_empty_rep_storage[];
			
			static _Rep&
			_S_empty_rep() _GLIBCXX_NOEXCEPT
			{ 
				// NB: Mild hack to avoid strict-aliasing warnings.  Note that
				// _S_empty_rep_storage is never modified and the punning should
				// be reasonably safe in this case.
				void* __p = reinterpret_cast<void*>(&_S_empty_rep_storage);
				return *reinterpret_cast<_Rep*>(__p);
			}
			
			bool
			_M_is_leaked() const _GLIBCXX_NOEXCEPT
			{
#if defined(__GTHREADS)
				// _M_refcount is mutated concurrently by _M_refcopy/_M_dispose,
				// so we need to use an atomic load. However, _M_is_leaked
				// predicate does not change concurrently (i.e. the string is either
				// leaked or not), so a relaxed load is enough.
				return __atomic_load_n(&this->_M_refcount, __ATOMIC_RELAXED) < 0;
#else
				return this->_M_refcount < 0;
#endif
			}
			
			bool
			_M_is_shared() const _GLIBCXX_NOEXCEPT
			{
#if defined(__GTHREADS)
				// _M_refcount is mutated concurrently by _M_refcopy/_M_dispose,
				// so we need to use an atomic load. Another thread can drop last
				// but one reference concurrently with this check, so we need this
				// load to be acquire to synchronize with release fetch_and_add in
				// _M_dispose.
				return __atomic_load_n(&this->_M_refcount, __ATOMIC_ACQUIRE) > 0;
#else
				return this->_M_refcount > 0;
#endif
			}
			
			void
			_M_set_leaked() _GLIBCXX_NOEXCEPT
			{ this->_M_refcount = -1; }
			
			void
			_M_set_sharable() _GLIBCXX_NOEXCEPT
			{ this->_M_refcount = 0; }
			
			void
			_M_set_length_and_sharable(size_type __n) _GLIBCXX_NOEXCEPT
			{
#if _GLIBCXX_FULLY_DYNAMIC_STRING == 0
				if (__builtin_expect(this != &_S_empty_rep(), false))
#endif
				{
					this->_M_set_sharable();  // One reference.
					this->_M_length = __n;
					traits_type::assign(this->_M_refdata()[__n], _S_terminal);
					// grrr. (per 21.3.4)
					// You cannot leave those LWG people alone for a second.
				}
			}
			
			_CharT*
			_M_refdata() throw()
			{ return reinterpret_cast<_CharT*>(this + 1); }
			
			_CharT*
			_M_grab(const _Alloc& __alloc1, const _Alloc& __alloc2)
			{
				return (!_M_is_leaked() && __alloc1 == __alloc2)
				? _M_refcopy() : _M_clone(__alloc1);
			}
			
			// Create & Destroy
			static _Rep*
			_S_create(size_type, size_type, const _Alloc&);
			
			void
			_M_dispose(const _Alloc& __a) _GLIBCXX_NOEXCEPT
			{
#if _GLIBCXX_FULLY_DYNAMIC_STRING == 0
				if (__builtin_expect(this != &_S_empty_rep(), false))
#endif
				{
					// Be race-detector-friendly.  For more info see bits/c++config.
					_GLIBCXX_SYNCHRONIZATION_HAPPENS_BEFORE(&this->_M_refcount);
					// Decrement of _M_refcount is acq_rel, because:
					// - all but last decrements need to release to synchronize with
					//   the last decrement that will delete the object.
					// - the last decrement needs to acquire to synchronize with
					//   all the previous decrements.
					// - last but one decrement needs to release to synchronize with
					//   the acquire load in _M_is_shared that will conclude that
					//   the object is not shared anymore.
					if (__gnu_cxx::__exchange_and_add_dispatch(&this->_M_refcount,
						-1) <= 0)
					{
						_GLIBCXX_SYNCHRONIZATION_HAPPENS_AFTER(&this->_M_refcount);
						_M_destroy(__a);
					}
				}
			}  // XXX MT
			
			void
			_M_destroy(const _Alloc&) throw();
			
			_CharT*
			_M_refcopy() throw()
			{
#if _GLIBCXX_FULLY_DYNAMIC_STRING == 0
				if (__builtin_expect(this != &_S_empty_rep(), false))
#endif
					__gnu_cxx::__atomic_add_dispatch(&this->_M_refcount, 1);
				return _M_refdata();
			}  // XXX MT
			
			_CharT*
			_M_clone(const _Alloc&, size_type __res = 0);
		};
		
		// Use empty-base optimization: http://www.cantrip.org/emptyopt.html
		struct _Alloc_hider : _Alloc
		{
			_Alloc_hider(_CharT* __dat, const _Alloc& __a) _GLIBCXX_NOEXCEPT
			: _Alloc(__a), _M_p(__dat) { }
			
			_CharT* _M_p; // The actual data.
		};
		
	public:
		// Data Members (public):
		// NB: This is an unsigned type, and thus represents the maximum
		// size that the allocator can hold.
		///  Value returned by various member functions when they fail.
		static const size_type	npos = static_cast<size_type>(-1);
		
	private:
		// Data Members (private):
		mutable _Alloc_hider	_M_dataplus;
		
		_CharT*
		_M_data() const _GLIBCXX_NOEXCEPT
		{ return  _M_dataplus._M_p; }
		
		_CharT*
		_M_data(_CharT* __p) _GLIBCXX_NOEXCEPT
		{ return (_M_dataplus._M_p = __p); }
		
		_Rep*
		_M_rep() const _GLIBCXX_NOEXCEPT
		{ return &((reinterpret_cast<_Rep*> (_M_data()))[-1]); }
		
		// For the internal use we have functions similar to `begin'/`end'
		// but they do not call _M_leak.
		iterator
		_M_ibegin() const _GLIBCXX_NOEXCEPT
		{ return iterator(_M_data()); }
		
		iterator
		_M_iend() const _GLIBCXX_NOEXCEPT
		{ return iterator(_M_data() + this->size()); }
		
		void
		_M_leak()    // for use in begin() & non-const op[]
		{
			if (!_M_rep()->_M_is_leaked())
				_M_leak_hard();
		}
		
		size_type
		_M_check(size_type __pos, const char* __s) const
		{
			if (__pos > this->size())
				__throw_out_of_range_fmt(__N("%s: __pos (which is %zu) > "
					"this->size() (which is %zu)"),
					__s, __pos, this->size());
			return __pos;
		}
		
		void
		_M_check_length(size_type __n1, size_type __n2, const char* __s) const
		{
			if (this->max_size() - (this->size() - __n1) < __n2)
				__throw_length_error(__N(__s));
		}
		
		// NB: _M_limit doesn't check for a bad __pos value.
		size_type
		_M_limit(size_type __pos, size_type __off) const _GLIBCXX_NOEXCEPT
		{
			const bool __testoff =  __off < this->size() - __pos;
			return __testoff ? __off : this->size() - __pos;
		}
		
		// True if _Rep and source do not overlap.
		bool
		_M_disjunct(const _CharT* __s) const _GLIBCXX_NOEXCEPT
		{
			return (less<const _CharT*>()(__s, _M_data())
				|| less<const _CharT*>()(_M_data() + this->size(), __s));
		}
		
		// When __n = 1 way faster than the general multichar
		// traits_type::copy/move/assign.
		static void
		_M_copy(_CharT* __d, const _CharT* __s, size_type __n) _GLIBCXX_NOEXCEPT
		{
			if (__n == 1)
				traits_type::assign(*__d, *__s);
			else
				traits_type::copy(__d, __s, __n);
		}
		
		static void
		_M_move(_CharT* __d, const _CharT* __s, size_type __n) _GLIBCXX_NOEXCEPT
		{
			if (__n == 1)
				traits_type::assign(*__d, *__s);
			else
				traits_type::move(__d, __s, __n);	  
		}
		
		static void
		_M_assign(_CharT* __d, size_type __n, _CharT __c) _GLIBCXX_NOEXCEPT
		{
			if (__n == 1)
				traits_type::assign(*__d, __c);
			else
				traits_type::assign(__d, __n, __c);	  
		}
		
		// _S_copy_chars is a separate template to permit specialization
		// to optimize for the common case of pointers as iterators.
		template<class _Iterator>
		static void
		_S_copy_chars(_CharT* __p, _Iterator __k1, _Iterator __k2)
		{
			for (; __k1 != __k2; ++__k1, (void)++__p)
				traits_type::assign(*__p, *__k1); // These types are off.
		}
		
		static void
		_S_copy_chars(_CharT* __p, iterator __k1, iterator __k2) _GLIBCXX_NOEXCEPT
		{ _S_copy_chars(__p, __k1.base(), __k2.base()); }
		
		static void
		_S_copy_chars(_CharT* __p, const_iterator __k1, const_iterator __k2)
		_GLIBCXX_NOEXCEPT
		{ _S_copy_chars(__p, __k1.base(), __k2.base()); }
		
		static void
		_S_copy_chars(_CharT* __p, _CharT* __k1, _CharT* __k2) _GLIBCXX_NOEXCEPT
		{ _M_copy(__p, __k1, __k2 - __k1); }
		
		static void
		_S_copy_chars(_CharT* __p, const _CharT* __k1, const _CharT* __k2)
		_GLIBCXX_NOEXCEPT
		{ _M_copy(__p, __k1, __k2 - __k1); }
		
		static int
		_S_compare(size_type __n1, size_type __n2) _GLIBCXX_NOEXCEPT
		{
			const difference_type __d = difference_type(__n1 - __n2);
			
			if (__d > __gnu_cxx::__numeric_traits<int>::__max)
				return __gnu_cxx::__numeric_traits<int>::__max;
			else if (__d < __gnu_cxx::__numeric_traits<int>::__min)
				return __gnu_cxx::__numeric_traits<int>::__min;
			else
				return int(__d);
		}
		
		void
		_M_mutate(size_type __pos, size_type __len1, size_type __len2);
		
		void
		_M_leak_hard();
		
		static _Rep&
		_S_empty_rep() _GLIBCXX_NOEXCEPT
		{ return _Rep::_S_empty_rep(); }
		
#if __cplusplus >= 201703L
		// A helper type for avoiding boiler-plate.
		typedef basic_string_view<_CharT, _Traits> __sv_type;
		
		template<typename _Tp, typename _Res>
		using _If_sv = enable_if_t<
		__and_<is_convertible<const _Tp&, __sv_type>,
		__not_<is_convertible<const _Tp*, const basic_string*>>,
		__not_<is_convertible<const _Tp&, const _CharT*>>>::value,
		_Res>;
		
		// Allows an implicit conversion to __sv_type.
		static __sv_type
		_S_to_string_view(__sv_type __svt) noexcept
		{ return __svt; }
		
		// Wraps a string_view by explicit conversion and thus
		// allows to add an internal constructor that does not
		// participate in overload resolution when a string_view
		// is provided.
		struct __sv_wrapper
		{
			explicit __sv_wrapper(__sv_type __sv) noexcept : _M_sv(__sv) { }
			__sv_type _M_sv;
		};
		
		/**
		 *  @brief  Only internally used: Construct string from a string view
		 *          wrapper.
		 *  @param  __svw  string view wrapper.
		 *  @param  __a  Allocator to use.
		 */
		explicit
		basic_string(__sv_wrapper __svw, const _Alloc& __a)
		: basic_string(__svw._M_sv.data(), __svw._M_sv.size(), __a) { }
#endif
		
	public:
		// Construct/copy/destroy:
		// NB: We overload ctors in some cases instead of using default
		// arguments, per 17.4.4.4 para. 2 item 2.
		
		/**
		 *  @brief  Default constructor creates an empty string.
		 */
		basic_string()
#if _GLIBCXX_FULLY_DYNAMIC_STRING == 0
		_GLIBCXX_NOEXCEPT
		: _M_dataplus(_S_empty_rep()._M_refdata(), _Alloc())
#else
		: _M_dataplus(_S_construct(size_type(), _CharT(), _Alloc()), _Alloc())
#endif
		{ }
		
		/**
		 *  @brief  Construct an empty string using allocator @a a.
		 */
		explicit
		basic_string(const _Alloc& __a)
		: _M_dataplus(_S_construct(size_type(), _CharT(), __a), __a)
		{ }
		
		// NB: per LWG issue 42, semantics different from IS:
		/**
		 *  @brief  Construct string with copy of value of @a str.
		 *  @param  __str  Source string.
		 */
		basic_string(const basic_string& __str)
		: _M_dataplus(__str._M_rep()->_M_grab(_Alloc(__str.get_allocator()),
			__str.get_allocator()),
			__str.get_allocator())
		{ }
		
		// _GLIBCXX_RESOLVE_LIB_DEFECTS
		// 2583. no way to supply an allocator for basic_string(str, pos)
		/**
		 *  @brief  Construct string as copy of a substring.
		 *  @param  __str  Source string.
		 *  @param  __pos  Index of first character to copy from.
		 *  @param  __a  Allocator to use.
		 */
		basic_string(const basic_string& __str, size_type __pos,
			const _Alloc& __a = _Alloc());
		
		/**
		 *  @brief  Construct string as copy of a substring.
		 *  @param  __str  Source string.
		 *  @param  __pos  Index of first character to copy from.
		 *  @param  __n  Number of characters to copy.
		 */
		basic_string(const basic_string& __str, size_type __pos,
			size_type __n);
		/**
		 *  @brief  Construct string as copy of a substring.
		 *  @param  __str  Source string.
		 *  @param  __pos  Index of first character to copy from.
		 *  @param  __n  Number of characters to copy.
		 *  @param  __a  Allocator to use.
		 */
		basic_string(const basic_string& __str, size_type __pos,
			size_type __n, const _Alloc& __a);
		
		/**
		 *  @brief  Construct string initialized by a character %array.
		 *  @param  __s  Source character %array.
		 *  @param  __n  Number of characters to copy.
		 *  @param  __a  Allocator to use (default is default allocator).
		 *
		 *  NB: @a __s must have at least @a __n characters, &apos;\\0&apos;
		 *  has no special meaning.
		 */
		basic_string(const _CharT* __s, size_type __n,
			const _Alloc& __a = _Alloc())
		: _M_dataplus(_S_construct(__s, __s + __n, __a), __a)
		{ }
		
		/**
		 *  @brief  Construct string as copy of a C string.
		 *  @param  __s  Source C string.
		 *  @param  __a  Allocator to use (default is default allocator).
		 */
#if __cpp_deduction_guides && ! defined _GLIBCXX_DEFINING_STRING_INSTANTIATIONS
		// _GLIBCXX_RESOLVE_LIB_DEFECTS
		// 3076. basic_string CTAD ambiguity
		template<typename = _RequireAllocator<_Alloc>>
#endif
		basic_string(const _CharT* __s, const _Alloc& __a = _Alloc())
		: _M_dataplus(_S_construct(__s, __s ? __s + traits_type::length(__s) :
			__s + npos, __a), __a)
		{ }
		
		/**
		 *  @brief  Construct string as multiple characters.
		 *  @param  __n  Number of characters.
		 *  @param  __c  Character to use.
		 *  @param  __a  Allocator to use (default is default allocator).
		 */
		basic_string(size_type __n, _CharT __c, const _Alloc& __a = _Alloc())
		: _M_dataplus(_S_construct(__n, __c, __a), __a)
		{ }
		
#if __cplusplus >= 201103L
		/**
		 *  @brief  Move construct string.
		 *  @param  __str  Source string.
		 *
		 *  The newly-created string contains the exact contents of @a __str.
		 *  @a __str is a valid, but unspecified string.
		 */
		basic_string(basic_string&& __str)
#if _GLIBCXX_FULLY_DYNAMIC_STRING == 0
		noexcept // FIXME C++11: should always be noexcept.
#endif
		: _M_dataplus(std::move(__str._M_dataplus))
		{
#if _GLIBCXX_FULLY_DYNAMIC_STRING == 0
			__str._M_data(_S_empty_rep()._M_refdata());
#else
			__str._M_data(_S_construct(size_type(), _CharT(), get_allocator()));
#endif
		}
		
		/**
		 *  @brief  Construct string from an initializer %list.
		 *  @param  __l  std::initializer_list of characters.
		 *  @param  __a  Allocator to use (default is default allocator).
		 */
		basic_string(initializer_list<_CharT> __l, const _Alloc& __a = _Alloc())
		: _M_dataplus(_S_construct(__l.begin(), __l.end(), __a), __a)
		{ }
		
		basic_string(const basic_string& __str, const _Alloc& __a)
		: _M_dataplus(__str._M_rep()->_M_grab(__a, __str.get_allocator()), __a)
		{ }
		
		basic_string(basic_string&& __str, const _Alloc& __a)
		: _M_dataplus(__str._M_data(), __a)
		{
			if (__a == __str.get_allocator())
			{
#if _GLIBCXX_FULLY_DYNAMIC_STRING == 0
				__str._M_data(_S_empty_rep()._M_refdata());
#else
				__str._M_data(_S_construct(size_type(), _CharT(), __a));
#endif
			}
			else
				_M_dataplus._M_p = _S_construct(__str.begin(), __str.end(), __a);
		}
#endif // C++11
		
		/**
		 *  @brief  Construct string as copy of a range.
		 *  @param  __beg  Start of range.
		 *  @param  __end  End of range.
		 *  @param  __a  Allocator to use (default is default allocator).
		 */
		template<class _InputIterator>
		basic_string(_InputIterator __beg, _InputIterator __end,
			const _Alloc& __a = _Alloc())
		: _M_dataplus(_S_construct(__beg, __end, __a), __a)
		{ }
		
#if __cplusplus >= 201703L
		/**
		 *  @brief  Construct string from a substring of a string_view.
		 *  @param  __t   Source object convertible to string view.
		 *  @param  __pos The index of the first character to copy from __t.
		 *  @param  __n   The number of characters to copy from __t.
		 *  @param  __a   Allocator to use.
		 */
		template<typename _Tp,
		typename = enable_if_t<is_convertible_v<const _Tp&, __sv_type>>>
		basic_string(const _Tp& __t, size_type __pos, size_type __n,
			const _Alloc& __a = _Alloc())
		: basic_string(_S_to_string_view(__t).substr(__pos, __n), __a) { }
		
		/**
		 *  @brief  Construct string from a string_view.
		 *  @param  __t  Source object convertible to string view.
		 *  @param  __a  Allocator to use (default is default allocator).
		 */
		template<typename _Tp, typename = _If_sv<_Tp, void>>
		explicit
		basic_string(const _Tp& __t, const _Alloc& __a = _Alloc())
		: basic_string(__sv_wrapper(_S_to_string_view(__t)), __a) { }
#endif // C++17
		
		/**
		 *  @brief  Destroy the string instance.
		 */
		~basic_string() _GLIBCXX_NOEXCEPT
		{ _M_rep()->_M_dispose(this->get_allocator()); }
		
		/**
		 *  @brief  Assign the value of @a str to this string.
		 *  @param  __str  Source string.
		 */
		basic_string&
		operator=(const basic_string& __str)
		{ return this->assign(__str); }
		
		/**
		 *  @brief  Copy contents of @a s into this string.
		 *  @param  __s  Source null-terminated string.
		 */
		basic_string&
		operator=(const _CharT* __s) 
		{ return this->assign(__s); }
		
		/**
		 *  @brief  Set value to string of length 1.
		 *  @param  __c  Source character.
		 *
		 *  Assigning to a character makes this string length 1 and
		 *  (*this)[0] == @a c.
		 */
		basic_string&
		operator=(_CharT __c) 
		{ 
			this->assign(1, __c); 
			return *this;
		}
		
#if __cplusplus >= 201103L
		/**
		 *  @brief  Move assign the value of @a str to this string.
		 *  @param  __str  Source string.
		 *
		 *  The contents of @a str are moved into this string (without copying).
		 *  @a str is a valid, but unspecified string.
		 */
		basic_string&
		operator=(basic_string&& __str)
		_GLIBCXX_NOEXCEPT_IF(allocator_traits<_Alloc>::is_always_equal::value)
		{
			// NB: DR 1204.
			this->swap(__str);
			return *this;
		}
		
		/**
		 *  @brief  Set value to string constructed from initializer %list.
		 *  @param  __l  std::initializer_list.
		 */
		basic_string&
		operator=(initializer_list<_CharT> __l)
		{
			this->assign(__l.begin(), __l.size());
			return *this;
		}
#endif // C++11
		
#if __cplusplus >= 201703L
		/**
		 *  @brief  Set value to string constructed from a string_view.
		 *  @param  __svt An object convertible to  string_view.
		 */
		template<typename _Tp>
		_If_sv<_Tp, basic_string&>
		operator=(const _Tp& __svt)
		{ return this->assign(__svt); }
		
		/**
		 *  @brief  Convert to a string_view.
		 *  @return A string_view.
		 */
		operator __sv_type() const noexcept
		{ return __sv_type(data(), size()); }
#endif // C++17
		
		// Iterators:
		/**
		 *  Returns a read/write iterator that points to the first character in
		 *  the %string.  Unshares the string.
		 */
		iterator
		begin() // FIXME C++11: should be noexcept.
		{
			_M_leak();
			return iterator(_M_data());
		}
		
		/**
		 *  Returns a read-only (constant) iterator that points to the first
		 *  character in the %string.
		 */
		const_iterator
		begin() const _GLIBCXX_NOEXCEPT
		{ return const_iterator(_M_data()); }
		
		/**
		 *  Returns a read/write iterator that points one past the last
		 *  character in the %string.  Unshares the string.
		 */
		iterator
		end() // FIXME C++11: should be noexcept.
		{
			_M_leak();
			return iterator(_M_data() + this->size());
		}
		
		/**
		 *  Returns a read-only (constant) iterator that points one past the
		 *  last character in the %string.
		 */
		const_iterator
		end() const _GLIBCXX_NOEXCEPT
		{ return const_iterator(_M_data() + this->size()); }
		
		/**
		 *  Returns a read/write reverse iterator that points to the last
		 *  character in the %string.  Iteration is done in reverse element
		 *  order.  Unshares the string.
		 */
		reverse_iterator
		rbegin() // FIXME C++11: should be noexcept.
		{ return reverse_iterator(this->end()); }
		
		/**
		 *  Returns a read-only (constant) reverse iterator that points
		 *  to the last character in the %string.  Iteration is done in
		 *  reverse element order.
		 */
		const_reverse_iterator
		rbegin() const _GLIBCXX_NOEXCEPT
		{ return const_reverse_iterator(this->end()); }
		
		/**
		 *  Returns a read/write reverse iterator that points to one before the
		 *  first character in the %string.  Iteration is done in reverse
		 *  element order.  Unshares the string.
		 */
		reverse_iterator
		rend() // FIXME C++11: should be noexcept.
		{ return reverse_iterator(this->begin()); }
		
		/**
		 *  Returns a read-only (constant) reverse iterator that points
		 *  to one before the first character in the %string.  Iteration
		 *  is done in reverse element order.
		 */
		const_reverse_iterator
		rend() const _GLIBCXX_NOEXCEPT
		{ return const_reverse_iterator(this->begin()); }
		
#if __cplusplus >= 201103L
		/**
		 *  Returns a read-only (constant) iterator that points to the first
		 *  character in the %string.
		 */
		const_iterator
		cbegin() const noexcept
		{ return const_iterator(this->_M_data()); }
		
		/**
		 *  Returns a read-only (constant) iterator that points one past the
		 *  last character in the %string.
		 */
		const_iterator
		cend() const noexcept
		{ return const_iterator(this->_M_data() + this->size()); }
		
		/**
		 *  Returns a read-only (constant) reverse iterator that points
		 *  to the last character in the %string.  Iteration is done in
		 *  reverse element order.
		 */
		const_reverse_iterator
		crbegin() const noexcept
		{ return const_reverse_iterator(this->end()); }
		
		/**
		 *  Returns a read-only (constant) reverse iterator that points
		 *  to one before the first character in the %string.  Iteration
		 *  is done in reverse element order.
		 */
		const_reverse_iterator
		crend() const noexcept
		{ return const_reverse_iterator(this->begin()); }
#endif
		
	public:
		// Capacity:
		///  Returns the number of characters in the string, not including any
		///  null-termination.
		size_type
		size() const _GLIBCXX_NOEXCEPT
		{ return _M_rep()->_M_length; }
		
		///  Returns the number of characters in the string, not including any
		///  null-termination.
		size_type
		length() const _GLIBCXX_NOEXCEPT
		{ return _M_rep()->_M_length; }
		
		///  Returns the size() of the largest possible %string.
		size_type
		max_size() const _GLIBCXX_NOEXCEPT
		{ return _Rep::_S_max_size; }
		
		/**
		 *  @brief  Resizes the %string to the specified number of characters.
		 *  @param  __n  Number of characters the %string should contain.
		 *  @param  __c  Character to fill any new elements.
		 *
		 *  This function will %resize the %string to the specified
		 *  number of characters.  If the number is smaller than the
		 *  %string's current size the %string is truncated, otherwise
		 *  the %string is extended and new elements are %set to @a __c.
		 */
		void
		resize(size_type __n, _CharT __c);
		
		/**
		 *  @brief  Resizes the %string to the specified number of characters.
		 *  @param  __n  Number of characters the %string should contain.
		 *
		 *  This function will resize the %string to the specified length.  If
		 *  the new size is smaller than the %string's current size the %string
		 *  is truncated, otherwise the %string is extended and new characters
		 *  are default-constructed.  For basic types such as char, this means
		 *  setting them to 0.
		 */
		void
		resize(size_type __n)
		{ this->resize(__n, _CharT()); }
		
#if __cplusplus >= 201103L
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
		///  A non-binding request to reduce capacity() to size().
		void
		shrink_to_fit() noexcept
		{ reserve(); }
#pragma GCC diagnostic pop
#endif
		
		/**
		 *  Returns the total number of characters that the %string can hold
		 *  before needing to allocate more memory.
		 */
		size_type
		capacity() const _GLIBCXX_NOEXCEPT
		{ return _M_rep()->_M_capacity; }
		
		/**
		 *  @brief  Attempt to preallocate enough memory for specified number of
		 *          characters.
		 *  @param  __res_arg  Number of characters required.
		 *  @throw  std::length_error  If @a __res_arg exceeds @c max_size().
		 *
		 *  This function attempts to reserve enough memory for the
		 *  %string to hold the specified number of characters.  If the
		 *  number requested is more than max_size(), length_error is
		 *  thrown.
		 *
		 *  The advantage of this function is that if optimal code is a
		 *  necessity and the user can determine the string length that will be
		 *  required, the user can reserve the memory in %advance, and thus
		 *  prevent a possible reallocation of memory and copying of %string
		 *  data.
		 */
		void
		reserve(size_type __res_arg);
		
		/// Equivalent to shrink_to_fit().
#if __cplusplus > 201703L
		[[deprecated("use shrink_to_fit() instead")]]
#endif
		void
		reserve();
		
		/**
		 *  Erases the string, making it empty.
		 */
#if _GLIBCXX_FULLY_DYNAMIC_STRING == 0
		void
		clear() _GLIBCXX_NOEXCEPT
		{
			if (_M_rep()->_M_is_shared())
			{
				_M_rep()->_M_dispose(this->get_allocator());
				_M_data(_S_empty_rep()._M_refdata());
			}
			else
				_M_rep()->_M_set_length_and_sharable(0);
		}
#else
		// PR 56166: this should not throw.
		void
		clear()
		{ _M_mutate(0, this->size(), 0); }
#endif
		
		/**
		 *  Returns true if the %string is empty.  Equivalent to 
		 *  <code>*this == ""</code>.
		 */
		_GLIBCXX_NODISCARD bool
		empty() const _GLIBCXX_NOEXCEPT
		{ return this->size() == 0; }
		
		// Element access:
		/**
		 *  @brief  Subscript access to the data contained in the %string.
		 *  @param  __pos  The index of the character to access.
		 *  @return  Read-only (constant) reference to the character.
		 *
		 *  This operator allows for easy, array-style, data access.
		 *  Note that data access with this operator is unchecked and
		 *  out_of_range lookups are not defined. (For checked lookups
		 *  see at().)
		 */
		const_reference
		operator[] (size_type __pos) const _GLIBCXX_NOEXCEPT
		{
			__glibcxx_assert(__pos <= size());
			return _M_data()[__pos];
		}
		
		/**
		 *  @brief  Subscript access to the data contained in the %string.
		 *  @param  __pos  The index of the character to access.
		 *  @return  Read/write reference to the character.
		 *
		 *  This operator allows for easy, array-style, data access.
		 *  Note that data access with this operator is unchecked and
		 *  out_of_range lookups are not defined. (For checked lookups
		 *  see at().)  Unshares the string.
		 */
		reference
		operator[](size_type __pos)
		{
			// Allow pos == size() both in C++98 mode, as v3 extension,
			// and in C++11 mode.
			__glibcxx_assert(__pos <= size());
			// In pedantic mode be strict in C++98 mode.
			_GLIBCXX_DEBUG_PEDASSERT(__cplusplus >= 201103L || __pos < size());
			_M_leak();
			return _M_data()[__pos];
		}
		
		/**
		 *  @brief  Provides access to the data contained in the %string.
		 *  @param __n The index of the character to access.
		 *  @return  Read-only (const) reference to the character.
		 *  @throw  std::out_of_range  If @a n is an invalid index.
		 *
		 *  This function provides for safer data access.  The parameter is
		 *  first checked that it is in the range of the string.  The function
		 *  throws out_of_range if the check fails.
		 */
		const_reference
		at(size_type __n) const
		{
			if (__n >= this->size())
				__throw_out_of_range_fmt(__N("basic_string::at: __n "
					"(which is %zu) >= this->size() "
					"(which is %zu)"),
					__n, this->size());
			return _M_data()[__n];
		}
		
		/**
		 *  @brief  Provides access to the data contained in the %string.
		 *  @param __n The index of the character to access.
		 *  @return  Read/write reference to the character.
		 *  @throw  std::out_of_range  If @a n is an invalid index.
		 *
		 *  This function provides for safer data access.  The parameter is
		 *  first checked that it is in the range of the string.  The function
		 *  throws out_of_range if the check fails.  Success results in
		 *  unsharing the string.
		 */
		reference
		at(size_type __n)
		{
			if (__n >= size())
				__throw_out_of_range_fmt(__N("basic_string::at: __n "
					"(which is %zu) >= this->size() "
					"(which is %zu)"),
					__n, this->size());
			_M_leak();
			return _M_data()[__n];
		}
		
#if __cplusplus >= 201103L
		/**
		 *  Returns a read/write reference to the data at the first
		 *  element of the %string.
		 */
		reference
		front()
		{
			__glibcxx_assert(!empty());
			return operator[](0);
		}
		
		/**
		 *  Returns a read-only (constant) reference to the data at the first
		 *  element of the %string.
		 */
		const_reference
		front() const noexcept
		{
			__glibcxx_assert(!empty());
			return operator[](0);
		}
		
		/**
		 *  Returns a read/write reference to the data at the last
		 *  element of the %string.
		 */
		reference
		back()
		{
			__glibcxx_assert(!empty());
			return operator[](this->size() - 1);
		}
		
		/**
		 *  Returns a read-only (constant) reference to the data at the
		 *  last element of the %string.
		 */
		const_reference
		back() const noexcept
		{
			__glibcxx_assert(!empty());
			return operator[](this->size() - 1);
		}
#endif
		
		// Modifiers:
		/**
		 *  @brief  Append a string to this string.
		 *  @param __str  The string to append.
		 *  @return  Reference to this string.
		 */
		basic_string&
		operator+=(const basic_string& __str)
		{ return this->append(__str); }
		
		/**
		 *  @brief  Append a C string.
		 *  @param __s  The C string to append.
		 *  @return  Reference to this string.
		 */
		basic_string&
		operator+=(const _CharT* __s)
		{ return this->append(__s); }
		
		/**
		 *  @brief  Append a character.
		 *  @param __c  The character to append.
		 *  @return  Reference to this string.
		 */
		basic_string&
		operator+=(_CharT __c)
		{ 
			this->push_back(__c);
			return *this;
		}
		
#if __cplusplus >= 201103L
		/**
		 *  @brief  Append an initializer_list of characters.
		 *  @param __l  The initializer_list of characters to be appended.
		 *  @return  Reference to this string.
		 */
		basic_string&
		operator+=(initializer_list<_CharT> __l)
		{ return this->append(__l.begin(), __l.size()); }
#endif // C++11
		
#if __cplusplus >= 201703L
		/**
		 *  @brief  Append a string_view.
		 *  @param __svt The object convertible to string_view to be appended.
		 *  @return  Reference to this string.
		 */
		template<typename _Tp>
		_If_sv<_Tp, basic_string&>
		operator+=(const _Tp& __svt)
		{ return this->append(__svt); }
#endif // C++17
		
		/**
		 *  @brief  Append a string to this string.
		 *  @param __str  The string to append.
		 *  @return  Reference to this string.
		 */
		basic_string&
		append(const basic_string& __str);
		
		/**
		 *  @brief  Append a substring.
		 *  @param __str  The string to append.
		 *  @param __pos  Index of the first character of str to append.
		 *  @param __n  The number of characters to append.
		 *  @return  Reference to this string.
		 *  @throw  std::out_of_range if @a __pos is not a valid index.
		 *
		 *  This function appends @a __n characters from @a __str
		 *  starting at @a __pos to this string.  If @a __n is is larger
		 *  than the number of available characters in @a __str, the
		 *  remainder of @a __str is appended.
		 */
		basic_string&
		append(const basic_string& __str, size_type __pos, size_type __n = npos);
		
		/**
		 *  @brief  Append a C substring.
		 *  @param __s  The C string to append.
		 *  @param __n  The number of characters to append.
		 *  @return  Reference to this string.
		 */
		basic_string&
		append(const _CharT* __s, size_type __n);
		
		/**
		 *  @brief  Append a C string.
		 *  @param __s  The C string to append.
		 *  @return  Reference to this string.
		 */
		basic_string&
		append(const _CharT* __s)
		{
			__glibcxx_requires_string(__s);
			return this->append(__s, traits_type::length(__s));
		}
		
		/**
		 *  @brief  Append multiple characters.
		 *  @param __n  The number of characters to append.
		 *  @param __c  The character to use.
		 *  @return  Reference to this string.
		 *
		 *  Appends __n copies of __c to this string.
		 */
		basic_string&
		append(size_type __n, _CharT __c);
		
#if __cplusplus >= 201103L
		/**
		 *  @brief  Append an initializer_list of characters.
		 *  @param __l  The initializer_list of characters to append.
		 *  @return  Reference to this string.
		 */
		basic_string&
		append(initializer_list<_CharT> __l)
		{ return this->append(__l.begin(), __l.size()); }
#endif // C++11
		
		/**
		 *  @brief  Append a range of characters.
		 *  @param __first  Iterator referencing the first character to append.
		 *  @param __last  Iterator marking the end of the range.
		 *  @return  Reference to this string.
		 *
		 *  Appends characters in the range [__first,__last) to this string.
		 */
		template<class _InputIterator>
		basic_string&
		append(_InputIterator __first, _InputIterator __last)
		{ return this->replace(_M_iend(), _M_iend(), __first, __last); }
		
#if __cplusplus >= 201703L
		/**
		 *  @brief  Append a string_view.
		 *  @param __svt The object convertible to string_view to be appended.
		 *  @return  Reference to this string.
		 */
		template<typename _Tp>
		_If_sv<_Tp, basic_string&>
		append(const _Tp& __svt)
		{
			__sv_type __sv = __svt;
			return this->append(__sv.data(), __sv.size());
		}
		
		/**
		 *  @brief  Append a range of characters from a string_view.
		 *  @param __svt The object convertible to string_view to be appended
		 *               from.
		 *  @param __pos The position in the string_view to append from.
		 *  @param __n   The number of characters to append from the string_view.
		 *  @return  Reference to this string.
		 */
		template<typename _Tp>
		_If_sv<_Tp, basic_string&>
		append(const _Tp& __svt, size_type __pos, size_type __n = npos)
		{
			__sv_type __sv = __svt;
			return append(__sv.data()
				+ std::__sv_check(__sv.size(), __pos, "basic_string::append"),
				std::__sv_limit(__sv.size(), __pos, __n));
		}
#endif // C++17
		
		/**
		 *  @brief  Append a single character.
		 *  @param __c  Character to append.
		 */
		void
		push_back(_CharT __c)
		{ 
			const size_type __len = 1 + this->size();
			if (__len > this->capacity() || _M_rep()->_M_is_shared())
				this->reserve(__len);
			traits_type::assign(_M_data()[this->size()], __c);
			_M_rep()->_M_set_length_and_sharable(__len);
		}
		
		/**
		 *  @brief  Set value to contents of another string.
		 *  @param  __str  Source string to use.
		 *  @return  Reference to this string.
		 */
		basic_string&
		assign(const basic_string& __str);
		
#if __cplusplus >= 201103L
		/**
		 *  @brief  Set value to contents of another string.
		 *  @param  __str  Source string to use.
		 *  @return  Reference to this string.
		 *
		 *  This function sets this string to the exact contents of @a __str.
		 *  @a __str is a valid, but unspecified string.
		 */
		basic_string&
		assign(basic_string&& __str)
		noexcept(allocator_traits<_Alloc>::is_always_equal::value)
		{
			this->swap(__str);
			return *this;
		}
#endif // C++11
		
		/**
		 *  @brief  Set value to a substring of a string.
		 *  @param __str  The string to use.
		 *  @param __pos  Index of the first character of str.
		 *  @param __n  Number of characters to use.
		 *  @return  Reference to this string.
		 *  @throw  std::out_of_range if @a pos is not a valid index.
		 *
		 *  This function sets this string to the substring of @a __str
		 *  consisting of @a __n characters at @a __pos.  If @a __n is
		 *  is larger than the number of available characters in @a
		 *  __str, the remainder of @a __str is used.
		 */
		basic_string&
		assign(const basic_string& __str, size_type __pos, size_type __n = npos)
		{ return this->assign(__str._M_data()
			+ __str._M_check(__pos, "basic_string::assign"),
			__str._M_limit(__pos, __n)); }
		
		/**
		 *  @brief  Set value to a C substring.
		 *  @param __s  The C string to use.
		 *  @param __n  Number of characters to use.
		 *  @return  Reference to this string.
		 *
		 *  This function sets the value of this string to the first @a __n
		 *  characters of @a __s.  If @a __n is is larger than the number of
		 *  available characters in @a __s, the remainder of @a __s is used.
		 */
		basic_string&
		assign(const _CharT* __s, size_type __n);
		
		/**
		 *  @brief  Set value to contents of a C string.
		 *  @param __s  The C string to use.
		 *  @return  Reference to this string.
		 *
		 *  This function sets the value of this string to the value of @a __s.
		 *  The data is copied, so there is no dependence on @a __s once the
		 *  function returns.
		 */
		basic_string&
		assign(const _CharT* __s)
		{
			__glibcxx_requires_string(__s);
			return this->assign(__s, traits_type::length(__s));
		}
		
		/**
		 *  @brief  Set value to multiple characters.
		 *  @param __n  Length of the resulting string.
		 *  @param __c  The character to use.
		 *  @return  Reference to this string.
		 *
		 *  This function sets the value of this string to @a __n copies of
		 *  character @a __c.
		 */
		basic_string&
		assign(size_type __n, _CharT __c)
		{ return _M_replace_aux(size_type(0), this->size(), __n, __c); }
		
		/**
		 *  @brief  Set value to a range of characters.
		 *  @param __first  Iterator referencing the first character to append.
		 *  @param __last  Iterator marking the end of the range.
		 *  @return  Reference to this string.
		 *
		 *  Sets value of string to characters in the range [__first,__last).
		 */
		template<class _InputIterator>
		basic_string&
		assign(_InputIterator __first, _InputIterator __last)
		{ return this->replace(_M_ibegin(), _M_iend(), __first, __last); }
		
#if __cplusplus >= 201103L
		/**
		 *  @brief  Set value to an initializer_list of characters.
		 *  @param __l  The initializer_list of characters to assign.
		 *  @return  Reference to this string.
		 */
		basic_string&
		assign(initializer_list<_CharT> __l)
		{ return this->assign(__l.begin(), __l.size()); }
#endif // C++11
		
#if __cplusplus >= 201703L
		/**
		 *  @brief  Set value from a string_view.
		 *  @param __svt The source object convertible to string_view.
		 *  @return  Reference to this string.
		 */
		template<typename _Tp>
		_If_sv<_Tp, basic_string&>
		assign(const _Tp& __svt)
		{
			__sv_type __sv = __svt;
			return this->assign(__sv.data(), __sv.size());
		}
		
		/**
		 *  @brief  Set value from a range of characters in a string_view.
		 *  @param __svt  The source object convertible to string_view.
		 *  @param __pos  The position in the string_view to assign from.
		 *  @param __n  The number of characters to assign.
		 *  @return  Reference to this string.
		 */
		template<typename _Tp>
		_If_sv<_Tp, basic_string&>
		assign(const _Tp& __svt, size_type __pos, size_type __n = npos)
		{
			__sv_type __sv = __svt;
			return assign(__sv.data()
				+ std::__sv_check(__sv.size(), __pos, "basic_string::assign"),
				std::__sv_limit(__sv.size(), __pos, __n));
		}
#endif // C++17
		
		/**
		 *  @brief  Insert multiple characters.
		 *  @param __p  Iterator referencing location in string to insert at.
		 *  @param __n  Number of characters to insert
		 *  @param __c  The character to insert.
		 *  @throw  std::length_error  If new length exceeds @c max_size().
		 *
		 *  Inserts @a __n copies of character @a __c starting at the
		 *  position referenced by iterator @a __p.  If adding
		 *  characters causes the length to exceed max_size(),
		 *  length_error is thrown.  The value of the string doesn't
		 *  change if an error is thrown.
		 */
		void
		insert(iterator __p, size_type __n, _CharT __c)
		{	this->replace(__p, __p, __n, __c);  }
		
		/**
		 *  @brief  Insert a range of characters.
		 *  @param __p  Iterator referencing location in string to insert at.
		 *  @param __beg  Start of range.
		 *  @param __end  End of range.
		 *  @throw  std::length_error  If new length exceeds @c max_size().
		 *
		 *  Inserts characters in range [__beg,__end).  If adding
		 *  characters causes the length to exceed max_size(),
		 *  length_error is thrown.  The value of the string doesn't
		 *  change if an error is thrown.
		 */
		template<class _InputIterator>
		void
		insert(iterator __p, _InputIterator __beg, _InputIterator __end)
		{ this->replace(__p, __p, __beg, __end); }
		
#if __cplusplus >= 201103L
		/**
		 *  @brief  Insert an initializer_list of characters.
		 *  @param __p  Iterator referencing location in string to insert at.
		 *  @param __l  The initializer_list of characters to insert.
		 *  @throw  std::length_error  If new length exceeds @c max_size().
		 */
		void
		insert(iterator __p, initializer_list<_CharT> __l)
		{
			_GLIBCXX_DEBUG_PEDASSERT(__p >= _M_ibegin() && __p <= _M_iend());
			this->insert(__p - _M_ibegin(), __l.begin(), __l.size());
		}
#endif // C++11
		
		/**
		 *  @brief  Insert value of a string.
		 *  @param __pos1  Position in string to insert at.
		 *  @param __str  The string to insert.
		 *  @return  Reference to this string.
		 *  @throw  std::length_error  If new length exceeds @c max_size().
		 *
		 *  Inserts value of @a __str starting at @a __pos1.  If adding
		 *  characters causes the length to exceed max_size(),
		 *  length_error is thrown.  The value of the string doesn't
		 *  change if an error is thrown.
		 */
		basic_string&
		insert(size_type __pos1, const basic_string& __str)
		{ return this->insert(__pos1, __str, size_type(0), __str.size()); }
		
		/**
		 *  @brief  Insert a substring.
		 *  @param __pos1  Position in string to insert at.
		 *  @param __str  The string to insert.
		 *  @param __pos2  Start of characters in str to insert.
		 *  @param __n  Number of characters to insert.
		 *  @return  Reference to this string.
		 *  @throw  std::length_error  If new length exceeds @c max_size().
		 *  @throw  std::out_of_range  If @a pos1 > size() or
		 *  @a __pos2 > @a str.size().
		 *
		 *  Starting at @a pos1, insert @a __n character of @a __str
		 *  beginning with @a __pos2.  If adding characters causes the
		 *  length to exceed max_size(), length_error is thrown.  If @a
		 *  __pos1 is beyond the end of this string or @a __pos2 is
		 *  beyond the end of @a __str, out_of_range is thrown.  The
		 *  value of the string doesn't change if an error is thrown.
		 */
		basic_string&
		insert(size_type __pos1, const basic_string& __str,
			size_type __pos2, size_type __n = npos)
		{ return this->insert(__pos1, __str._M_data()
			+ __str._M_check(__pos2, "basic_string::insert"),
			__str._M_limit(__pos2, __n)); }
		
		/**
		 *  @brief  Insert a C substring.
		 *  @param __pos  Position in string to insert at.
		 *  @param __s  The C string to insert.
		 *  @param __n  The number of characters to insert.
		 *  @return  Reference to this string.
		 *  @throw  std::length_error  If new length exceeds @c max_size().
		 *  @throw  std::out_of_range  If @a __pos is beyond the end of this
		 *  string.
		 *
		 *  Inserts the first @a __n characters of @a __s starting at @a
		 *  __pos.  If adding characters causes the length to exceed
		 *  max_size(), length_error is thrown.  If @a __pos is beyond
		 *  end(), out_of_range is thrown.  The value of the string
		 *  doesn't change if an error is thrown.
		 */
		basic_string&
		insert(size_type __pos, const _CharT* __s, size_type __n);
		
		/**
		 *  @brief  Insert a C string.
		 *  @param __pos  Position in string to insert at.
		 *  @param __s  The C string to insert.
		 *  @return  Reference to this string.
		 *  @throw  std::length_error  If new length exceeds @c max_size().
		 *  @throw  std::out_of_range  If @a pos is beyond the end of this
		 *  string.
		 *
		 *  Inserts the first @a n characters of @a __s starting at @a __pos.  If
		 *  adding characters causes the length to exceed max_size(),
		 *  length_error is thrown.  If @a __pos is beyond end(), out_of_range is
		 *  thrown.  The value of the string doesn't change if an error is
		 *  thrown.
		 */
		basic_string&
		insert(size_type __pos, const _CharT* __s)
		{
			__glibcxx_requires_string(__s);
			return this->insert(__pos, __s, traits_type::length(__s));
		}
		
		/**
		 *  @brief  Insert multiple characters.
		 *  @param __pos  Index in string to insert at.
		 *  @param __n  Number of characters to insert
		 *  @param __c  The character to insert.
		 *  @return  Reference to this string.
		 *  @throw  std::length_error  If new length exceeds @c max_size().
		 *  @throw  std::out_of_range  If @a __pos is beyond the end of this
		 *  string.
		 *
		 *  Inserts @a __n copies of character @a __c starting at index
		 *  @a __pos.  If adding characters causes the length to exceed
		 *  max_size(), length_error is thrown.  If @a __pos > length(),
		 *  out_of_range is thrown.  The value of the string doesn't
		 *  change if an error is thrown.
		 */
		basic_string&
		insert(size_type __pos, size_type __n, _CharT __c)
		{ return _M_replace_aux(_M_check(__pos, "basic_string::insert"),
			size_type(0), __n, __c); }
		
		/**
		 *  @brief  Insert one character.
		 *  @param __p  Iterator referencing position in string to insert at.
		 *  @param __c  The character to insert.
		 *  @return  Iterator referencing newly inserted char.
		 *  @throw  std::length_error  If new length exceeds @c max_size().
		 *
		 *  Inserts character @a __c at position referenced by @a __p.
		 *  If adding character causes the length to exceed max_size(),
		 *  length_error is thrown.  If @a __p is beyond end of string,
		 *  out_of_range is thrown.  The value of the string doesn't
		 *  change if an error is thrown.
		 */
		iterator
		insert(iterator __p, _CharT __c)
		{
			_GLIBCXX_DEBUG_PEDASSERT(__p >= _M_ibegin() && __p <= _M_iend());
			const size_type __pos = __p - _M_ibegin();
			_M_replace_aux(__pos, size_type(0), size_type(1), __c);
			_M_rep()->_M_set_leaked();
			return iterator(_M_data() + __pos);
		}
		
#if __cplusplus >= 201703L
		/**
		 *  @brief  Insert a string_view.
		 *  @param __pos  Position in string to insert at.
		 *  @param __svt  The object convertible to string_view to insert.
		 *  @return  Reference to this string.
		 */
		template<typename _Tp>
		_If_sv<_Tp, basic_string&>
		insert(size_type __pos, const _Tp& __svt)
		{
			__sv_type __sv = __svt;
			return this->insert(__pos, __sv.data(), __sv.size());
		}
		
		/**
		 *  @brief  Insert a string_view.
		 *  @param __pos1  Position in string to insert at.
		 *  @param __svt   The object convertible to string_view to insert from.
		 *  @param __pos2  Position in string_view to insert from.
		 *  @param __n    The number of characters to insert.
		 *  @return  Reference to this string.
		 */
		template<typename _Tp>
		_If_sv<_Tp, basic_string&>
		insert(size_type __pos1, const _Tp& __svt,
			size_type __pos2, size_type __n = npos)
		{
			__sv_type __sv = __svt;
			return this->replace(__pos1, size_type(0), __sv.data()
				+ std::__sv_check(__sv.size(), __pos2, "basic_string::insert"),
				std::__sv_limit(__sv.size(), __pos2, __n));
		}
#endif // C++17
		
		/**
		 *  @brief  Remove characters.
		 *  @param __pos  Index of first character to remove (default 0).
		 *  @param __n  Number of characters to remove (default remainder).
		 *  @return  Reference to this string.
		 *  @throw  std::out_of_range  If @a pos is beyond the end of this
		 *  string.
		 *
		 *  Removes @a __n characters from this string starting at @a
		 *  __pos.  The length of the string is reduced by @a __n.  If
		 *  there are < @a __n characters to remove, the remainder of
		 *  the string is truncated.  If @a __p is beyond end of string,
		 *  out_of_range is thrown.  The value of the string doesn't
		 *  change if an error is thrown.
		 */
		basic_string&
		erase(size_type __pos = 0, size_type __n = npos)
		{ 
			_M_mutate(_M_check(__pos, "basic_string::erase"),
				_M_limit(__pos, __n), size_type(0));
			return *this;
		}
		
		/**
		 *  @brief  Remove one character.
		 *  @param __position  Iterator referencing the character to remove.
		 *  @return  iterator referencing same location after removal.
		 *
		 *  Removes the character at @a __position from this string. The value
		 *  of the string doesn't change if an error is thrown.
		 */
		iterator
		erase(iterator __position)
		{
			_GLIBCXX_DEBUG_PEDASSERT(__position >= _M_ibegin()
				&& __position < _M_iend());
			const size_type __pos = __position - _M_ibegin();
			_M_mutate(__pos, size_type(1), size_type(0));
			_M_rep()->_M_set_leaked();
			return iterator(_M_data() + __pos);
		}
		
		/**
		 *  @brief  Remove a range of characters.
		 *  @param __first  Iterator referencing the first character to remove.
		 *  @param __last  Iterator referencing the end of the range.
		 *  @return  Iterator referencing location of first after removal.
		 *
		 *  Removes the characters in the range [first,last) from this string.
		 *  The value of the string doesn't change if an error is thrown.
		 */
		iterator
		erase(iterator __first, iterator __last);
		
#if __cplusplus >= 201103L
		/**
		 *  @brief  Remove the last character.
		 *
		 *  The string must be non-empty.
		 */
		void
		pop_back() // FIXME C++11: should be noexcept.
		{
			__glibcxx_assert(!empty());
			erase(size() - 1, 1);
		}
#endif // C++11
		
		/**
		 *  @brief  Replace characters with value from another string.
		 *  @param __pos  Index of first character to replace.
		 *  @param __n  Number of characters to be replaced.
		 *  @param __str  String to insert.
		 *  @return  Reference to this string.
		 *  @throw  std::out_of_range  If @a pos is beyond the end of this
		 *  string.
		 *  @throw  std::length_error  If new length exceeds @c max_size().
		 *
		 *  Removes the characters in the range [__pos,__pos+__n) from
		 *  this string.  In place, the value of @a __str is inserted.
		 *  If @a __pos is beyond end of string, out_of_range is thrown.
		 *  If the length of the result exceeds max_size(), length_error
		 *  is thrown.  The value of the string doesn't change if an
		 *  error is thrown.
		 */
		basic_string&
		replace(size_type __pos, size_type __n, const basic_string& __str)
		{ return this->replace(__pos, __n, __str._M_data(), __str.size()); }
		
		/**
		 *  @brief  Replace characters with value from another string.
		 *  @param __pos1  Index of first character to replace.
		 *  @param __n1  Number of characters to be replaced.
		 *  @param __str  String to insert.
		 *  @param __pos2  Index of first character of str to use.
		 *  @param __n2  Number of characters from str to use.
		 *  @return  Reference to this string.
		 *  @throw  std::out_of_range  If @a __pos1 > size() or @a __pos2 >
		 *  __str.size().
		 *  @throw  std::length_error  If new length exceeds @c max_size().
		 *
		 *  Removes the characters in the range [__pos1,__pos1 + n) from this
		 *  string.  In place, the value of @a __str is inserted.  If @a __pos is
		 *  beyond end of string, out_of_range is thrown.  If the length of the
		 *  result exceeds max_size(), length_error is thrown.  The value of the
		 *  string doesn't change if an error is thrown.
		 */
		basic_string&
		replace(size_type __pos1, size_type __n1, const basic_string& __str,
			size_type __pos2, size_type __n2 = npos)
		{ return this->replace(__pos1, __n1, __str._M_data()
			+ __str._M_check(__pos2, "basic_string::replace"),
			__str._M_limit(__pos2, __n2)); }
		
		/**
		 *  @brief  Replace characters with value of a C substring.
		 *  @param __pos  Index of first character to replace.
		 *  @param __n1  Number of characters to be replaced.
		 *  @param __s  C string to insert.
		 *  @param __n2  Number of characters from @a s to use.
		 *  @return  Reference to this string.
		 *  @throw  std::out_of_range  If @a pos1 > size().
		 *  @throw  std::length_error  If new length exceeds @c max_size().
		 *
		 *  Removes the characters in the range [__pos,__pos + __n1)
		 *  from this string.  In place, the first @a __n2 characters of
		 *  @a __s are inserted, or all of @a __s if @a __n2 is too large.  If
		 *  @a __pos is beyond end of string, out_of_range is thrown.  If
		 *  the length of result exceeds max_size(), length_error is
		 *  thrown.  The value of the string doesn't change if an error
		 *  is thrown.
		 */
		basic_string&
		replace(size_type __pos, size_type __n1, const _CharT* __s,
			size_type __n2);
		
		/**
		 *  @brief  Replace characters with value of a C string.
		 *  @param __pos  Index of first character to replace.
		 *  @param __n1  Number of characters to be replaced.
		 *  @param __s  C string to insert.
		 *  @return  Reference to this string.
		 *  @throw  std::out_of_range  If @a pos > size().
		 *  @throw  std::length_error  If new length exceeds @c max_size().
		 *
		 *  Removes the characters in the range [__pos,__pos + __n1)
		 *  from this string.  In place, the characters of @a __s are
		 *  inserted.  If @a __pos is beyond end of string, out_of_range
		 *  is thrown.  If the length of result exceeds max_size(),
		 *  length_error is thrown.  The value of the string doesn't
		 *  change if an error is thrown.
		 */
		basic_string&
		replace(size_type __pos, size_type __n1, const _CharT* __s)
		{
			__glibcxx_requires_string(__s);
			return this->replace(__pos, __n1, __s, traits_type::length(__s));
		}
		
		/**
		 *  @brief  Replace characters with multiple characters.
		 *  @param __pos  Index of first character to replace.
		 *  @param __n1  Number of characters to be replaced.
		 *  @param __n2  Number of characters to insert.
		 *  @param __c  Character to insert.
		 *  @return  Reference to this string.
		 *  @throw  std::out_of_range  If @a __pos > size().
		 *  @throw  std::length_error  If new length exceeds @c max_size().
		 *
		 *  Removes the characters in the range [pos,pos + n1) from this
		 *  string.  In place, @a __n2 copies of @a __c are inserted.
		 *  If @a __pos is beyond end of string, out_of_range is thrown.
		 *  If the length of result exceeds max_size(), length_error is
		 *  thrown.  The value of the string doesn't change if an error
		 *  is thrown.
		 */
		basic_string&
		replace(size_type __pos, size_type __n1, size_type __n2, _CharT __c)
		{ return _M_replace_aux(_M_check(__pos, "basic_string::replace"),
			_M_limit(__pos, __n1), __n2, __c); }
		
		/**
		 *  @brief  Replace range of characters with string.
		 *  @param __i1  Iterator referencing start of range to replace.
		 *  @param __i2  Iterator referencing end of range to replace.
		 *  @param __str  String value to insert.
		 *  @return  Reference to this string.
		 *  @throw  std::length_error  If new length exceeds @c max_size().
		 *
		 *  Removes the characters in the range [__i1,__i2).  In place,
		 *  the value of @a __str is inserted.  If the length of result
		 *  exceeds max_size(), length_error is thrown.  The value of
		 *  the string doesn't change if an error is thrown.
		 */
		basic_string&
		replace(iterator __i1, iterator __i2, const basic_string& __str)
		{ return this->replace(__i1, __i2, __str._M_data(), __str.size()); }
		
		/**
		 *  @brief  Replace range of characters with C substring.
		 *  @param __i1  Iterator referencing start of range to replace.
		 *  @param __i2  Iterator referencing end of range to replace.
		 *  @param __s  C string value to insert.
		 *  @param __n  Number of characters from s to insert.
		 *  @return  Reference to this string.
		 *  @throw  std::length_error  If new length exceeds @c max_size().
		 *
		 *  Removes the characters in the range [__i1,__i2).  In place,
		 *  the first @a __n characters of @a __s are inserted.  If the
		 *  length of result exceeds max_size(), length_error is thrown.
		 *  The value of the string doesn't change if an error is
		 *  thrown.
		 */
		basic_string&
		replace(iterator __i1, iterator __i2, const _CharT* __s, size_type __n)
		{
			_GLIBCXX_DEBUG_PEDASSERT(_M_ibegin() <= __i1 && __i1 <= __i2
				&& __i2 <= _M_iend());
			return this->replace(__i1 - _M_ibegin(), __i2 - __i1, __s, __n);
		}
		
		/**
		 *  @brief  Replace range of characters with C string.
		 *  @param __i1  Iterator referencing start of range to replace.
		 *  @param __i2  Iterator referencing end of range to replace.
		 *  @param __s  C string value to insert.
		 *  @return  Reference to this string.
		 *  @throw  std::length_error  If new length exceeds @c max_size().
		 *
		 *  Removes the characters in the range [__i1,__i2).  In place,
		 *  the characters of @a __s are inserted.  If the length of
		 *  result exceeds max_size(), length_error is thrown.  The
		 *  value of the string doesn't change if an error is thrown.
		 */
		basic_string&
		replace(iterator __i1, iterator __i2, const _CharT* __s)
		{
			__glibcxx_requires_string(__s);
			return this->replace(__i1, __i2, __s, traits_type::length(__s));
		}
		
		/**
		 *  @brief  Replace range of characters with multiple characters
		 *  @param __i1  Iterator referencing start of range to replace.
		 *  @param __i2  Iterator referencing end of range to replace.
		 *  @param __n  Number of characters to insert.
		 *  @param __c  Character to insert.
		 *  @return  Reference to this string.
		 *  @throw  std::length_error  If new length exceeds @c max_size().
		 *
		 *  Removes the characters in the range [__i1,__i2).  In place,
		 *  @a __n copies of @a __c are inserted.  If the length of
		 *  result exceeds max_size(), length_error is thrown.  The
		 *  value of the string doesn't change if an error is thrown.
		 */
		basic_string&
		replace(iterator __i1, iterator __i2, size_type __n, _CharT __c)
		{
			_GLIBCXX_DEBUG_PEDASSERT(_M_ibegin() <= __i1 && __i1 <= __i2
				&& __i2 <= _M_iend());
			return _M_replace_aux(__i1 - _M_ibegin(), __i2 - __i1, __n, __c);
		}
		
		/**
		 *  @brief  Replace range of characters with range.
		 *  @param __i1  Iterator referencing start of range to replace.
		 *  @param __i2  Iterator referencing end of range to replace.
		 *  @param __k1  Iterator referencing start of range to insert.
		 *  @param __k2  Iterator referencing end of range to insert.
		 *  @return  Reference to this string.
		 *  @throw  std::length_error  If new length exceeds @c max_size().
		 *
		 *  Removes the characters in the range [__i1,__i2).  In place,
		 *  characters in the range [__k1,__k2) are inserted.  If the
		 *  length of result exceeds max_size(), length_error is thrown.
		 *  The value of the string doesn't change if an error is
		 *  thrown.
		 */
		template<class _InputIterator>
		basic_string&
		replace(iterator __i1, iterator __i2,
			_InputIterator __k1, _InputIterator __k2)
		{
			_GLIBCXX_DEBUG_PEDASSERT(_M_ibegin() <= __i1 && __i1 <= __i2
				&& __i2 <= _M_iend());
			__glibcxx_requires_valid_range(__k1, __k2);
			typedef typename std::__is_integer<_InputIterator>::__type _Integral;
			return _M_replace_dispatch(__i1, __i2, __k1, __k2, _Integral());
		}
		
		// Specializations for the common case of pointer and iterator:
		// useful to avoid the overhead of temporary buffering in _M_replace.
		basic_string&
		replace(iterator __i1, iterator __i2, _CharT* __k1, _CharT* __k2)
		{
			_GLIBCXX_DEBUG_PEDASSERT(_M_ibegin() <= __i1 && __i1 <= __i2
				&& __i2 <= _M_iend());
			__glibcxx_requires_valid_range(__k1, __k2);
			return this->replace(__i1 - _M_ibegin(), __i2 - __i1,
				__k1, __k2 - __k1);
		}
		
		basic_string&
		replace(iterator __i1, iterator __i2,
			const _CharT* __k1, const _CharT* __k2)
		{
			_GLIBCXX_DEBUG_PEDASSERT(_M_ibegin() <= __i1 && __i1 <= __i2
				&& __i2 <= _M_iend());
			__glibcxx_requires_valid_range(__k1, __k2);
			return this->replace(__i1 - _M_ibegin(), __i2 - __i1,
				__k1, __k2 - __k1);
		}
		
		basic_string&
		replace(iterator __i1, iterator __i2, iterator __k1, iterator __k2)
		{
			_GLIBCXX_DEBUG_PEDASSERT(_M_ibegin() <= __i1 && __i1 <= __i2
				&& __i2 <= _M_iend());
			__glibcxx_requires_valid_range(__k1, __k2);
			return this->replace(__i1 - _M_ibegin(), __i2 - __i1,
				__k1.base(), __k2 - __k1);
		}
		
		basic_string&
		replace(iterator __i1, iterator __i2,
			const_iterator __k1, const_iterator __k2)
		{
			_GLIBCXX_DEBUG_PEDASSERT(_M_ibegin() <= __i1 && __i1 <= __i2
				&& __i2 <= _M_iend());
			__glibcxx_requires_valid_range(__k1, __k2);
			return this->replace(__i1 - _M_ibegin(), __i2 - __i1,
				__k1.base(), __k2 - __k1);
		}
		
#if __cplusplus >= 201103L
		/**
		 *  @brief  Replace range of characters with initializer_list.
		 *  @param __i1  Iterator referencing start of range to replace.
		 *  @param __i2  Iterator referencing end of range to replace.
		 *  @param __l  The initializer_list of characters to insert.
		 *  @return  Reference to this string.
		 *  @throw  std::length_error  If new length exceeds @c max_size().
		 *
		 *  Removes the characters in the range [__i1,__i2).  In place,
		 *  characters in the range [__k1,__k2) are inserted.  If the
		 *  length of result exceeds max_size(), length_error is thrown.
		 *  The value of the string doesn't change if an error is
		 *  thrown.
		 */
		basic_string& replace(iterator __i1, iterator __i2,
			initializer_list<_CharT> __l)
		{ return this->replace(__i1, __i2, __l.begin(), __l.end()); }
#endif // C++11
		
#if __cplusplus >= 201703L
		/**
		 *  @brief  Replace range of characters with string_view.
		 *  @param __pos  The position to replace at.
		 *  @param __n    The number of characters to replace.
		 *  @param __svt  The object convertible to string_view to insert.
		 *  @return  Reference to this string.
		 */
		template<typename _Tp>
		_If_sv<_Tp, basic_string&>
		replace(size_type __pos, size_type __n, const _Tp& __svt)
		{
			__sv_type __sv = __svt;
			return this->replace(__pos, __n, __sv.data(), __sv.size());
		}
		
		/**
		 *  @brief  Replace range of characters with string_view.
		 *  @param __pos1  The position to replace at.
		 *  @param __n1    The number of characters to replace.
		 *  @param __svt   The object convertible to string_view to insert from.
		 *  @param __pos2  The position in the string_view to insert from.
		 *  @param __n2    The number of characters to insert.
		 *  @return  Reference to this string.
		 */
		template<typename _Tp>
		_If_sv<_Tp, basic_string&>
		replace(size_type __pos1, size_type __n1, const _Tp& __svt,
			size_type __pos2, size_type __n2 = npos)
		{
			__sv_type __sv = __svt;
			return this->replace(__pos1, __n1,
				__sv.data()
				+ std::__sv_check(__sv.size(), __pos2, "basic_string::replace"),
				std::__sv_limit(__sv.size(), __pos2, __n2));
		}
		
		/**
		 *  @brief  Replace range of characters with string_view.
		 *  @param __i1    An iterator referencing the start position
		  to replace at.
		 *  @param __i2    An iterator referencing the end position
		  for the replace.
		 *  @param __svt   The object convertible to string_view to insert from.
		 *  @return  Reference to this string.
		 */
		template<typename _Tp>
		_If_sv<_Tp, basic_string&>
		replace(const_iterator __i1, const_iterator __i2, const _Tp& __svt)
		{
			__sv_type __sv = __svt;
			return this->replace(__i1 - begin(), __i2 - __i1, __sv);
		}
#endif // C++17
		
	private:
		template<class _Integer>
		basic_string&
		_M_replace_dispatch(iterator __i1, iterator __i2, _Integer __n,
			_Integer __val, __true_type)
		{ return _M_replace_aux(__i1 - _M_ibegin(), __i2 - __i1, __n, __val); }
		
		template<class _InputIterator>
		basic_string&
		_M_replace_dispatch(iterator __i1, iterator __i2, _InputIterator __k1,
			_InputIterator __k2, __false_type);
		
		basic_string&
		_M_replace_aux(size_type __pos1, size_type __n1, size_type __n2,
			_CharT __c);
		
		basic_string&
		_M_replace_safe(size_type __pos1, size_type __n1, const _CharT* __s,
			size_type __n2);
		
		// _S_construct_aux is used to implement the 21.3.1 para 15 which
		// requires special behaviour if _InIter is an integral type
		template<class _InIterator>
		static _CharT*
		_S_construct_aux(_InIterator __beg, _InIterator __end,
			const _Alloc& __a, __false_type)
		{
			typedef typename iterator_traits<_InIterator>::iterator_category _Tag;
			return _S_construct(__beg, __end, __a, _Tag());
		}
		
		// _GLIBCXX_RESOLVE_LIB_DEFECTS
		// 438. Ambiguity in the "do the right thing" clause
		template<class _Integer>
		static _CharT*
		_S_construct_aux(_Integer __beg, _Integer __end,
			const _Alloc& __a, __true_type)
		{ return _S_construct_aux_2(static_cast<size_type>(__beg),
			__end, __a); }
		
		static _CharT*
		_S_construct_aux_2(size_type __req, _CharT __c, const _Alloc& __a)
		{ return _S_construct(__req, __c, __a); }
		
		template<class _InIterator>
		static _CharT*
		_S_construct(_InIterator __beg, _InIterator __end, const _Alloc& __a)
		{
			typedef typename std::__is_integer<_InIterator>::__type _Integral;
			return _S_construct_aux(__beg, __end, __a, _Integral());
		}
		
		// For Input Iterators, used in istreambuf_iterators, etc.
		template<class _InIterator>
		static _CharT*
		_S_construct(_InIterator __beg, _InIterator __end, const _Alloc& __a,
			input_iterator_tag);
		
		// For forward_iterators up to random_access_iterators, used for
		// string::iterator, _CharT*, etc.
		template<class _FwdIterator>
		static _CharT*
		_S_construct(_FwdIterator __beg, _FwdIterator __end, const _Alloc& __a,
			forward_iterator_tag);
		
		static _CharT*
		_S_construct(size_type __req, _CharT __c, const _Alloc& __a);
		
	public:
		
		/**
		 *  @brief  Copy substring into C string.
		 *  @param __s  C string to copy value into.
		 *  @param __n  Number of characters to copy.
		 *  @param __pos  Index of first character to copy.
		 *  @return  Number of characters actually copied
		 *  @throw  std::out_of_range  If __pos > size().
		 *
		 *  Copies up to @a __n characters starting at @a __pos into the
		 *  C string @a __s.  If @a __pos is %greater than size(),
		 *  out_of_range is thrown.
		 */
		size_type
		copy(_CharT* __s, size_type __n, size_type __pos = 0) const;
		
		/**
		 *  @brief  Swap contents with another string.
		 *  @param __s  String to swap with.
		 *
		 *  Exchanges the contents of this string with that of @a __s in constant
		 *  time.
		 */
		void
		swap(basic_string& __s)
		_GLIBCXX_NOEXCEPT_IF(allocator_traits<_Alloc>::is_always_equal::value);
		
		// String operations:
		/**
		 *  @brief  Return const pointer to null-terminated contents.
		 *
		 *  This is a handle to internal data.  Do not modify or dire things may
		 *  happen.
		 */
		const _CharT*
		c_str() const _GLIBCXX_NOEXCEPT
		{ return _M_data(); }
		
		/**
		 *  @brief  Return const pointer to contents.
		 *
		 *  This is a pointer to internal data.  It is undefined to modify
		 *  the contents through the returned pointer. To get a pointer that
		 *  allows modifying the contents use @c &str[0] instead,
		 *  (or in C++17 the non-const @c str.data() overload).
		 */
		const _CharT*
		data() const _GLIBCXX_NOEXCEPT
		{ return _M_data(); }
		
#if __cplusplus >= 201703L
		/**
		 *  @brief  Return non-const pointer to contents.
		 *
		 *  This is a pointer to the character sequence held by the string.
		 *  Modifying the characters in the sequence is allowed.
		 */
		_CharT*
		data() noexcept
		{
			_M_leak();
			return _M_data();
		}
#endif
		
		/**
		 *  @brief  Return copy of allocator used to construct this string.
		 */
		allocator_type
		get_allocator() const _GLIBCXX_NOEXCEPT
		{ return _M_dataplus; }
		
		/**
		 *  @brief  Find position of a C substring.
		 *  @param __s  C string to locate.
		 *  @param __pos  Index of character to search from.
		 *  @param __n  Number of characters from @a s to search for.
		 *  @return  Index of start of first occurrence.
		 *
		 *  Starting from @a __pos, searches forward for the first @a
		 *  __n characters in @a __s within this string.  If found,
		 *  returns the index where it begins.  If not found, returns
		 *  npos.
		 */
		size_type
		find(const _CharT* __s, size_type __pos, size_type __n) const
		_GLIBCXX_NOEXCEPT;
		
		/**
		 *  @brief  Find position of a string.
		 *  @param __str  String to locate.
		 *  @param __pos  Index of character to search from (default 0).
		 *  @return  Index of start of first occurrence.
		 *
		 *  Starting from @a __pos, searches forward for value of @a __str within
		 *  this string.  If found, returns the index where it begins.  If not
		 *  found, returns npos.
		 */
		size_type
		find(const basic_string& __str, size_type __pos = 0) const
		_GLIBCXX_NOEXCEPT
		{ return this->find(__str.data(), __pos, __str.size()); }
		
		/**
		 *  @brief  Find position of a C string.
		 *  @param __s  C string to locate.
		 *  @param __pos  Index of character to search from (default 0).
		 *  @return  Index of start of first occurrence.
		 *
		 *  Starting from @a __pos, searches forward for the value of @a
		 *  __s within this string.  If found, returns the index where
		 *  it begins.  If not found, returns npos.
		 */
		size_type
		find(const _CharT* __s, size_type __pos = 0) const _GLIBCXX_NOEXCEPT
		{
			__glibcxx_requires_string(__s);
			return this->find(__s, __pos, traits_type::length(__s));
		}
		
		/**
		 *  @brief  Find position of a character.
		 *  @param __c  Character to locate.
		 *  @param __pos  Index of character to search from (default 0).
		 *  @return  Index of first occurrence.
		 *
		 *  Starting from @a __pos, searches forward for @a __c within
		 *  this string.  If found, returns the index where it was
		 *  found.  If not found, returns npos.
		 */
		size_type
		find(_CharT __c, size_type __pos = 0) const _GLIBCXX_NOEXCEPT;
		
#if __cplusplus >= 201703L
		/**
		 *  @brief  Find position of a string_view.
		 *  @param __svt  The object convertible to string_view to locate.
		 *  @param __pos  Index of character to search from (default 0).
		 *  @return  Index of start of first occurrence.
		 */
		template<typename _Tp>
		_If_sv<_Tp, size_type>
		find(const _Tp& __svt, size_type __pos = 0) const
		noexcept(is_same<_Tp, __sv_type>::value)
		{
			__sv_type __sv = __svt;
			return this->find(__sv.data(), __pos, __sv.size());
		}
#endif // C++17
		
		/**
		 *  @brief  Find last position of a string.
		 *  @param __str  String to locate.
		 *  @param __pos  Index of character to search back from (default end).
		 *  @return  Index of start of last occurrence.
		 *
		 *  Starting from @a __pos, searches backward for value of @a
		 *  __str within this string.  If found, returns the index where
		 *  it begins.  If not found, returns npos.
		 */
		size_type
		rfind(const basic_string& __str, size_type __pos = npos) const
		_GLIBCXX_NOEXCEPT
		{ return this->rfind(__str.data(), __pos, __str.size()); }
		
		/**
		 *  @brief  Find last position of a C substring.
		 *  @param __s  C string to locate.
		 *  @param __pos  Index of character to search back from.
		 *  @param __n  Number of characters from s to search for.
		 *  @return  Index of start of last occurrence.
		 *
		 *  Starting from @a __pos, searches backward for the first @a
		 *  __n characters in @a __s within this string.  If found,
		 *  returns the index where it begins.  If not found, returns
		 *  npos.
		 */
		size_type
		rfind(const _CharT* __s, size_type __pos, size_type __n) const
		_GLIBCXX_NOEXCEPT;
		
		/**
		 *  @brief  Find last position of a C string.
		 *  @param __s  C string to locate.
		 *  @param __pos  Index of character to start search at (default end).
		 *  @return  Index of start of  last occurrence.
		 *
		 *  Starting from @a __pos, searches backward for the value of
		 *  @a __s within this string.  If found, returns the index
		 *  where it begins.  If not found, returns npos.
		 */
		size_type
		rfind(const _CharT* __s, size_type __pos = npos) const _GLIBCXX_NOEXCEPT
		{
			__glibcxx_requires_string(__s);
			return this->rfind(__s, __pos, traits_type::length(__s));
		}
		
		/**
		 *  @brief  Find last position of a character.
		 *  @param __c  Character to locate.
		 *  @param __pos  Index of character to search back from (default end).
		 *  @return  Index of last occurrence.
		 *
		 *  Starting from @a __pos, searches backward for @a __c within
		 *  this string.  If found, returns the index where it was
		 *  found.  If not found, returns npos.
		 */
		size_type
		rfind(_CharT __c, size_type __pos = npos) const _GLIBCXX_NOEXCEPT;
		
#if __cplusplus >= 201703L
		/**
		 *  @brief  Find last position of a string_view.
		 *  @param __svt  The object convertible to string_view to locate.
		 *  @param __pos  Index of character to search back from (default end).
		 *  @return  Index of start of last occurrence.
		 */
		template<typename _Tp>
		_If_sv<_Tp, size_type>
		rfind(const _Tp& __svt, size_type __pos = npos) const
		noexcept(is_same<_Tp, __sv_type>::value)
		{
			__sv_type __sv = __svt;
			return this->rfind(__sv.data(), __pos, __sv.size());
		}
#endif // C++17
		
		/**
		 *  @brief  Find position of a character of string.
		 *  @param __str  String containing characters to locate.
		 *  @param __pos  Index of character to search from (default 0).
		 *  @return  Index of first occurrence.
		 *
		 *  Starting from @a __pos, searches forward for one of the
		 *  characters of @a __str within this string.  If found,
		 *  returns the index where it was found.  If not found, returns
		 *  npos.
		 */
		size_type
		find_first_of(const basic_string& __str, size_type __pos = 0) const
		_GLIBCXX_NOEXCEPT
		{ return this->find_first_of(__str.data(), __pos, __str.size()); }
		
		/**
		 *  @brief  Find position of a character of C substring.
		 *  @param __s  String containing characters to locate.
		 *  @param __pos  Index of character to search from.
		 *  @param __n  Number of characters from s to search for.
		 *  @return  Index of first occurrence.
		 *
		 *  Starting from @a __pos, searches forward for one of the
		 *  first @a __n characters of @a __s within this string.  If
		 *  found, returns the index where it was found.  If not found,
		 *  returns npos.
		 */
		size_type
		find_first_of(const _CharT* __s, size_type __pos, size_type __n) const
		_GLIBCXX_NOEXCEPT;
		
		/**
		 *  @brief  Find position of a character of C string.
		 *  @param __s  String containing characters to locate.
		 *  @param __pos  Index of character to search from (default 0).
		 *  @return  Index of first occurrence.
		 *
		 *  Starting from @a __pos, searches forward for one of the
		 *  characters of @a __s within this string.  If found, returns
		 *  the index where it was found.  If not found, returns npos.
		 */
		size_type
		find_first_of(const _CharT* __s, size_type __pos = 0) const
		_GLIBCXX_NOEXCEPT
		{
			__glibcxx_requires_string(__s);
			return this->find_first_of(__s, __pos, traits_type::length(__s));
		}
		
		/**
		 *  @brief  Find position of a character.
		 *  @param __c  Character to locate.
		 *  @param __pos  Index of character to search from (default 0).
		 *  @return  Index of first occurrence.
		 *
		 *  Starting from @a __pos, searches forward for the character
		 *  @a __c within this string.  If found, returns the index
		 *  where it was found.  If not found, returns npos.
		 *
		 *  Note: equivalent to find(__c, __pos).
		 */
		size_type
		find_first_of(_CharT __c, size_type __pos = 0) const _GLIBCXX_NOEXCEPT
		{ return this->find(__c, __pos); }
		
#if __cplusplus >= 201703L
		/**
		 *  @brief  Find position of a character of a string_view.
		 *  @param __svt  An object convertible to string_view containing
		 *                characters to locate.
		 *  @param __pos  Index of character to search from (default 0).
		 *  @return  Index of first occurrence.
		 */
		template<typename _Tp>
		_If_sv<_Tp, size_type>
		find_first_of(const _Tp& __svt, size_type __pos = 0) const
		noexcept(is_same<_Tp, __sv_type>::value)
		{
			__sv_type __sv = __svt;
			return this->find_first_of(__sv.data(), __pos, __sv.size());
		}
#endif // C++17
		
		/**
		 *  @brief  Find last position of a character of string.
		 *  @param __str  String containing characters to locate.
		 *  @param __pos  Index of character to search back from (default end).
		 *  @return  Index of last occurrence.
		 *
		 *  Starting from @a __pos, searches backward for one of the
		 *  characters of @a __str within this string.  If found,
		 *  returns the index where it was found.  If not found, returns
		 *  npos.
		 */
		size_type
		find_last_of(const basic_string& __str, size_type __pos = npos) const
		_GLIBCXX_NOEXCEPT
		{ return this->find_last_of(__str.data(), __pos, __str.size()); }
		
		/**
		 *  @brief  Find last position of a character of C substring.
		 *  @param __s  C string containing characters to locate.
		 *  @param __pos  Index of character to search back from.
		 *  @param __n  Number of characters from s to search for.
		 *  @return  Index of last occurrence.
		 *
		 *  Starting from @a __pos, searches backward for one of the
		 *  first @a __n characters of @a __s within this string.  If
		 *  found, returns the index where it was found.  If not found,
		 *  returns npos.
		 */
		size_type
		find_last_of(const _CharT* __s, size_type __pos, size_type __n) const
		_GLIBCXX_NOEXCEPT;
		
		/**
		 *  @brief  Find last position of a character of C string.
		 *  @param __s  C string containing characters to locate.
		 *  @param __pos  Index of character to search back from (default end).
		 *  @return  Index of last occurrence.
		 *
		 *  Starting from @a __pos, searches backward for one of the
		 *  characters of @a __s within this string.  If found, returns
		 *  the index where it was found.  If not found, returns npos.
		 */
		size_type
		find_last_of(const _CharT* __s, size_type __pos = npos) const
		_GLIBCXX_NOEXCEPT
		{
			__glibcxx_requires_string(__s);
			return this->find_last_of(__s, __pos, traits_type::length(__s));
		}
		
		/**
		 *  @brief  Find last position of a character.
		 *  @param __c  Character to locate.
		 *  @param __pos  Index of character to search back from (default end).
		 *  @return  Index of last occurrence.
		 *
		 *  Starting from @a __pos, searches backward for @a __c within
		 *  this string.  If found, returns the index where it was
		 *  found.  If not found, returns npos.
		 *
		 *  Note: equivalent to rfind(__c, __pos).
		 */
		size_type
		find_last_of(_CharT __c, size_type __pos = npos) const _GLIBCXX_NOEXCEPT
		{ return this->rfind(__c, __pos); }
		
#if __cplusplus >= 201703L
		/**
		 *  @brief  Find last position of a character of string.
		 *  @param __svt  An object convertible to string_view containing
		 *                characters to locate.
		 *  @param __pos  Index of character to search back from (default end).
		 *  @return  Index of last occurrence.
		 */
		template<typename _Tp>
		_If_sv<_Tp, size_type>
		find_last_of(const _Tp& __svt, size_type __pos = npos) const
		noexcept(is_same<_Tp, __sv_type>::value)
		{
			__sv_type __sv = __svt;
			return this->find_last_of(__sv.data(), __pos, __sv.size());
		}
#endif // C++17
		
		/**
		 *  @brief  Find position of a character not in string.
		 *  @param __str  String containing characters to avoid.
		 *  @param __pos  Index of character to search from (default 0).
		 *  @return  Index of first occurrence.
		 *
		 *  Starting from @a __pos, searches forward for a character not contained
		 *  in @a __str within this string.  If found, returns the index where it
		 *  was found.  If not found, returns npos.
		 */
		size_type
		find_first_not_of(const basic_string& __str, size_type __pos = 0) const
		_GLIBCXX_NOEXCEPT
		{ return this->find_first_not_of(__str.data(), __pos, __str.size()); }
		
		/**
		 *  @brief  Find position of a character not in C substring.
		 *  @param __s  C string containing characters to avoid.
		 *  @param __pos  Index of character to search from.
		 *  @param __n  Number of characters from __s to consider.
		 *  @return  Index of first occurrence.
		 *
		 *  Starting from @a __pos, searches forward for a character not
		 *  contained in the first @a __n characters of @a __s within
		 *  this string.  If found, returns the index where it was
		 *  found.  If not found, returns npos.
		 */
		size_type
		find_first_not_of(const _CharT* __s, size_type __pos,
			size_type __n) const _GLIBCXX_NOEXCEPT;
		
		/**
		 *  @brief  Find position of a character not in C string.
		 *  @param __s  C string containing characters to avoid.
		 *  @param __pos  Index of character to search from (default 0).
		 *  @return  Index of first occurrence.
		 *
		 *  Starting from @a __pos, searches forward for a character not
		 *  contained in @a __s within this string.  If found, returns
		 *  the index where it was found.  If not found, returns npos.
		 */
		size_type
		find_first_not_of(const _CharT* __s, size_type __pos = 0) const
		_GLIBCXX_NOEXCEPT
		{
			__glibcxx_requires_string(__s);
			return this->find_first_not_of(__s, __pos, traits_type::length(__s));
		}
		
		/**
		 *  @brief  Find position of a different character.
		 *  @param __c  Character to avoid.
		 *  @param __pos  Index of character to search from (default 0).
		 *  @return  Index of first occurrence.
		 *
		 *  Starting from @a __pos, searches forward for a character
		 *  other than @a __c within this string.  If found, returns the
		 *  index where it was found.  If not found, returns npos.
		 */
		size_type
		find_first_not_of(_CharT __c, size_type __pos = 0) const
		_GLIBCXX_NOEXCEPT;
		
#if __cplusplus >= 201703L
		/**
		 *  @brief  Find position of a character not in a string_view.
		 *  @param __svt  An object convertible to string_view containing
		 *                characters to avoid.
		 *  @param __pos  Index of character to search from (default 0).
		 *  @return  Index of first occurrence.
		 */
		template<typename _Tp>
		_If_sv<_Tp, size_type>
		find_first_not_of(const _Tp& __svt, size_type __pos = 0) const
		noexcept(is_same<_Tp, __sv_type>::value)
		{
			__sv_type __sv = __svt;
			return this->find_first_not_of(__sv.data(), __pos, __sv.size());
		}
#endif // C++17
		
		/**
		 *  @brief  Find last position of a character not in string.
		 *  @param __str  String containing characters to avoid.
		 *  @param __pos  Index of character to search back from (default end).
		 *  @return  Index of last occurrence.
		 *
		 *  Starting from @a __pos, searches backward for a character
		 *  not contained in @a __str within this string.  If found,
		 *  returns the index where it was found.  If not found, returns
		 *  npos.
		 */
		size_type
		find_last_not_of(const basic_string& __str, size_type __pos = npos) const
		_GLIBCXX_NOEXCEPT
		{ return this->find_last_not_of(__str.data(), __pos, __str.size()); }
		
		/**
		 *  @brief  Find last position of a character not in C substring.
		 *  @param __s  C string containing characters to avoid.
		 *  @param __pos  Index of character to search back from.
		 *  @param __n  Number of characters from s to consider.
		 *  @return  Index of last occurrence.
		 *
		 *  Starting from @a __pos, searches backward for a character not
		 *  contained in the first @a __n characters of @a __s within this string.
		 *  If found, returns the index where it was found.  If not found,
		 *  returns npos.
		 */
		size_type
		find_last_not_of(const _CharT* __s, size_type __pos,
			size_type __n) const _GLIBCXX_NOEXCEPT;
		/**
		 *  @brief  Find last position of a character not in C string.
		 *  @param __s  C string containing characters to avoid.
		 *  @param __pos  Index of character to search back from (default end).
		 *  @return  Index of last occurrence.
		 *
		 *  Starting from @a __pos, searches backward for a character
		 *  not contained in @a __s within this string.  If found,
		 *  returns the index where it was found.  If not found, returns
		 *  npos.
		 */
		size_type
		find_last_not_of(const _CharT* __s, size_type __pos = npos) const
		_GLIBCXX_NOEXCEPT
		{
			__glibcxx_requires_string(__s);
			return this->find_last_not_of(__s, __pos, traits_type::length(__s));
		}
		
		/**
		 *  @brief  Find last position of a different character.
		 *  @param __c  Character to avoid.
		 *  @param __pos  Index of character to search back from (default end).
		 *  @return  Index of last occurrence.
		 *
		 *  Starting from @a __pos, searches backward for a character other than
		 *  @a __c within this string.  If found, returns the index where it was
		 *  found.  If not found, returns npos.
		 */
		size_type
		find_last_not_of(_CharT __c, size_type __pos = npos) const
		_GLIBCXX_NOEXCEPT;
		
#if __cplusplus >= 201703L
		/**
		 *  @brief  Find last position of a character not in a string_view.
		 *  @param __svt  An object convertible to string_view containing
		 *                characters to avoid.
		 *  @param __pos  Index of character to search back from (default end).
		 *  @return  Index of last occurrence.
		 */
		template<typename _Tp>
		_If_sv<_Tp, size_type>
		find_last_not_of(const _Tp& __svt, size_type __pos = npos) const
		noexcept(is_same<_Tp, __sv_type>::value)
		{
			__sv_type __sv = __svt;
			return this->find_last_not_of(__sv.data(), __pos, __sv.size());
		}
#endif // C++17
		
		/**
		 *  @brief  Get a substring.
		 *  @param __pos  Index of first character (default 0).
		 *  @param __n  Number of characters in substring (default remainder).
		 *  @return  The new string.
		 *  @throw  std::out_of_range  If __pos > size().
		 *
		 *  Construct and return a new string using the @a __n
		 *  characters starting at @a __pos.  If the string is too
		 *  short, use the remainder of the characters.  If @a __pos is
		 *  beyond the end of the string, out_of_range is thrown.
		 */
		basic_string
		substr(size_type __pos = 0, size_type __n = npos) const
		{ return basic_string(*this,
			_M_check(__pos, "basic_string::substr"), __n); }
		
		/**
		 *  @brief  Compare to a string.
		 *  @param __str  String to compare against.
		 *  @return  Integer < 0, 0, or > 0.
		 *
		 *  Returns an integer < 0 if this string is ordered before @a
		 *  __str, 0 if their values are equivalent, or > 0 if this
		 *  string is ordered after @a __str.  Determines the effective
		 *  length rlen of the strings to compare as the smallest of
		 *  size() and str.size().  The function then compares the two
		 *  strings by calling traits::compare(data(), str.data(),rlen).
		 *  If the result of the comparison is nonzero returns it,
		 *  otherwise the shorter one is ordered first.
		 */
		int
		compare(const basic_string& __str) const
		{
			const size_type __size = this->size();
			const size_type __osize = __str.size();
			const size_type __len = std::min(__size, __osize);
			
			int __r = traits_type::compare(_M_data(), __str.data(), __len);
			if (!__r)
				__r = _S_compare(__size, __osize);
			return __r;
		}
		
#if __cplusplus >= 201703L
		/**
		 *  @brief  Compare to a string_view.
		 *  @param __svt An object convertible to string_view to compare against.
		 *  @return  Integer < 0, 0, or > 0.
		 */
		template<typename _Tp>
		_If_sv<_Tp, int>
		compare(const _Tp& __svt) const
		noexcept(is_same<_Tp, __sv_type>::value)
		{
			__sv_type __sv = __svt;
			const size_type __size = this->size();
			const size_type __osize = __sv.size();
			const size_type __len = std::min(__size, __osize);
			
			int __r = traits_type::compare(_M_data(), __sv.data(), __len);
			if (!__r)
				__r = _S_compare(__size, __osize);
			return __r;
		}
		
		/**
		 *  @brief  Compare to a string_view.
		 *  @param __pos  A position in the string to start comparing from.
		 *  @param __n  The number of characters to compare.
		 *  @param __svt  An object convertible to string_view to compare
		 *                against.
		 *  @return  Integer < 0, 0, or > 0.
		 */
		template<typename _Tp>
		_If_sv<_Tp, int>
		compare(size_type __pos, size_type __n, const _Tp& __svt) const
		noexcept(is_same<_Tp, __sv_type>::value)
		{
			__sv_type __sv = __svt;
			return __sv_type(*this).substr(__pos, __n).compare(__sv);
		}
		
		/**
		 *  @brief  Compare to a string_view.
		 *  @param __pos1  A position in the string to start comparing from.
		 *  @param __n1  The number of characters to compare.
		 *  @param __svt   An object convertible to string_view to compare
		 *                 against.
		 *  @param __pos2  A position in the string_view to start comparing from.
		 *  @param __n2  The number of characters to compare.
		 *  @return  Integer < 0, 0, or > 0.
		 */
		template<typename _Tp>
		_If_sv<_Tp, int>
		compare(size_type __pos1, size_type __n1, const _Tp& __svt,
			size_type __pos2, size_type __n2 = npos) const
		noexcept(is_same<_Tp, __sv_type>::value)
		{
			__sv_type __sv = __svt;
			return __sv_type(*this)
			.substr(__pos1, __n1).compare(__sv.substr(__pos2, __n2));
		}
#endif // C++17
		
		/**
		 *  @brief  Compare substring to a string.
		 *  @param __pos  Index of first character of substring.
		 *  @param __n  Number of characters in substring.
		 *  @param __str  String to compare against.
		 *  @return  Integer < 0, 0, or > 0.
		 *
		 *  Form the substring of this string from the @a __n characters
		 *  starting at @a __pos.  Returns an integer < 0 if the
		 *  substring is ordered before @a __str, 0 if their values are
		 *  equivalent, or > 0 if the substring is ordered after @a
		 *  __str.  Determines the effective length rlen of the strings
		 *  to compare as the smallest of the length of the substring
		 *  and @a __str.size().  The function then compares the two
		 *  strings by calling
		 *  traits::compare(substring.data(),str.data(),rlen).  If the
		 *  result of the comparison is nonzero returns it, otherwise
		 *  the shorter one is ordered first.
		 */
		int
		compare(size_type __pos, size_type __n, const basic_string& __str) const;
		
		/**
		 *  @brief  Compare substring to a substring.
		 *  @param __pos1  Index of first character of substring.
		 *  @param __n1  Number of characters in substring.
		 *  @param __str  String to compare against.
		 *  @param __pos2  Index of first character of substring of str.
		 *  @param __n2  Number of characters in substring of str.
		 *  @return  Integer < 0, 0, or > 0.
		 *
		 *  Form the substring of this string from the @a __n1
		 *  characters starting at @a __pos1.  Form the substring of @a
		 *  __str from the @a __n2 characters starting at @a __pos2.
		 *  Returns an integer < 0 if this substring is ordered before
		 *  the substring of @a __str, 0 if their values are equivalent,
		 *  or > 0 if this substring is ordered after the substring of
		 *  @a __str.  Determines the effective length rlen of the
		 *  strings to compare as the smallest of the lengths of the
		 *  substrings.  The function then compares the two strings by
		 *  calling
		 *  traits::compare(substring.data(),str.substr(pos2,n2).data(),rlen).
		 *  If the result of the comparison is nonzero returns it,
		 *  otherwise the shorter one is ordered first.
		 */
		int
		compare(size_type __pos1, size_type __n1, const basic_string& __str,
			size_type __pos2, size_type __n2 = npos) const;
		
		/**
		 *  @brief  Compare to a C string.
		 *  @param __s  C string to compare against.
		 *  @return  Integer < 0, 0, or > 0.
		 *
		 *  Returns an integer < 0 if this string is ordered before @a __s, 0 if
		 *  their values are equivalent, or > 0 if this string is ordered after
		 *  @a __s.  Determines the effective length rlen of the strings to
		 *  compare as the smallest of size() and the length of a string
		 *  constructed from @a __s.  The function then compares the two strings
		 *  by calling traits::compare(data(),s,rlen).  If the result of the
		 *  comparison is nonzero returns it, otherwise the shorter one is
		 *  ordered first.
		 */
		int
		compare(const _CharT* __s) const _GLIBCXX_NOEXCEPT;
		
		// _GLIBCXX_RESOLVE_LIB_DEFECTS
		// 5 String::compare specification questionable
		/**
		 *  @brief  Compare substring to a C string.
		 *  @param __pos  Index of first character of substring.
		 *  @param __n1  Number of characters in substring.
		 *  @param __s  C string to compare against.
		 *  @return  Integer < 0, 0, or > 0.
		 *
		 *  Form the substring of this string from the @a __n1
		 *  characters starting at @a pos.  Returns an integer < 0 if
		 *  the substring is ordered before @a __s, 0 if their values
		 *  are equivalent, or > 0 if the substring is ordered after @a
		 *  __s.  Determines the effective length rlen of the strings to
		 *  compare as the smallest of the length of the substring and
		 *  the length of a string constructed from @a __s.  The
		 *  function then compares the two string by calling
		 *  traits::compare(substring.data(),__s,rlen).  If the result of
		 *  the comparison is nonzero returns it, otherwise the shorter
		 *  one is ordered first.
		 */
		int
		compare(size_type __pos, size_type __n1, const _CharT* __s) const;
		
		/**
		 *  @brief  Compare substring against a character %array.
		 *  @param __pos  Index of first character of substring.
		 *  @param __n1  Number of characters in substring.
		 *  @param __s  character %array to compare against.
		 *  @param __n2  Number of characters of s.
		 *  @return  Integer < 0, 0, or > 0.
		 *
		 *  Form the substring of this string from the @a __n1
		 *  characters starting at @a __pos.  Form a string from the
		 *  first @a __n2 characters of @a __s.  Returns an integer < 0
		 *  if this substring is ordered before the string from @a __s,
		 *  0 if their values are equivalent, or > 0 if this substring
		 *  is ordered after the string from @a __s.  Determines the
		 *  effective length rlen of the strings to compare as the
		 *  smallest of the length of the substring and @a __n2.  The
		 *  function then compares the two strings by calling
		 *  traits::compare(substring.data(),s,rlen).  If the result of
		 *  the comparison is nonzero returns it, otherwise the shorter
		 *  one is ordered first.
		 *
		 *  NB: s must have at least n2 characters, &apos;\\0&apos; has
		 *  no special meaning.
		 */
		int
		compare(size_type __pos, size_type __n1, const _CharT* __s,
			size_type __n2) const;
		
#if __cplusplus > 201703L
		bool
		starts_with(basic_string_view<_CharT, _Traits> __x) const noexcept
		{ return __sv_type(this->data(), this->size()).starts_with(__x); }
		
		bool
		starts_with(_CharT __x) const noexcept
		{ return __sv_type(this->data(), this->size()).starts_with(__x); }
		
		bool
		starts_with(const _CharT* __x) const noexcept
		{ return __sv_type(this->data(), this->size()).starts_with(__x); }
		
		bool
		ends_with(basic_string_view<_CharT, _Traits> __x) const noexcept
		{ return __sv_type(this->data(), this->size()).ends_with(__x); }
		
		bool
		ends_with(_CharT __x) const noexcept
		{ return __sv_type(this->data(), this->size()).ends_with(__x); }
		
		bool
		ends_with(const _CharT* __x) const noexcept
		{ return __sv_type(this->data(), this->size()).ends_with(__x); }
#endif // C++20
		
#if __cplusplus > 202011L
		bool
		contains(basic_string_view<_CharT, _Traits> __x) const noexcept
		{ return __sv_type(this->data(), this->size()).contains(__x); }
		
		bool
		contains(_CharT __x) const noexcept
		{ return __sv_type(this->data(), this->size()).contains(__x); }
		
		bool
		contains(const _CharT* __x) const noexcept
		{ return __sv_type(this->data(), this->size()).contains(__x); }
#endif // C++23
		
# ifdef _GLIBCXX_TM_TS_INTERNAL
		friend void
		::_txnal_cow_string_C1_for_exceptions(void* that, const char* s,
			void* exc);
		friend const char*
		::_txnal_cow_string_c_str(const void *that);
		friend void
		::_txnal_cow_string_D1(void *that);
		friend void
		::_txnal_cow_string_D1_commit(void *that);
# endif
	};
#endif  // !_GLIBCXX_USE_CXX11_ABI
	
#if __cpp_deduction_guides >= 201606
	_GLIBCXX_BEGIN_NAMESPACE_CXX11
	template<typename _InputIterator, typename _CharT
	= typename iterator_traits<_InputIterator>::value_type,
	typename _Allocator = allocator<_CharT>,
	typename = _RequireInputIter<_InputIterator>,
	typename = _RequireAllocator<_Allocator>>
	basic_string(_InputIterator, _InputIterator, _Allocator = _Allocator())
	-> basic_string<_CharT, char_traits<_CharT>, _Allocator>;
	
	// _GLIBCXX_RESOLVE_LIB_DEFECTS
	// 3075. basic_string needs deduction guides from basic_string_view
	template<typename _CharT, typename _Traits,
	typename _Allocator = allocator<_CharT>,
	typename = _RequireAllocator<_Allocator>>
	basic_string(basic_string_view<_CharT, _Traits>, const _Allocator& = _Allocator())
	-> basic_string<_CharT, _Traits, _Allocator>;
	
	template<typename _CharT, typename _Traits,
	typename _Allocator = allocator<_CharT>,
	typename = _RequireAllocator<_Allocator>>
	basic_string(basic_string_view<_CharT, _Traits>,
		typename basic_string<_CharT, _Traits, _Allocator>::size_type,
		typename basic_string<_CharT, _Traits, _Allocator>::size_type,
		const _Allocator& = _Allocator())
	-> basic_string<_CharT, _Traits, _Allocator>;
	_GLIBCXX_END_NAMESPACE_CXX11
#endif
	
	// operator+
	/**
	 *  @brief  Concatenate two strings.
	 *  @param __lhs  First string.
	 *  @param __rhs  Last string.
	 *  @return  New string with value of @a __lhs followed by @a __rhs.
	 */
	template<typename _CharT, typename _Traits, typename _Alloc>
	basic_string<_CharT, _Traits, _Alloc>
	operator+(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
		const basic_string<_CharT, _Traits, _Alloc>& __rhs)
	{
		basic_string<_CharT, _Traits, _Alloc> __str(__lhs);
		__str.append(__rhs);
		return __str;
	}
	
	/**
	 *  @brief  Concatenate C string and string.
	 *  @param __lhs  First string.
	 *  @param __rhs  Last string.
	 *  @return  New string with value of @a __lhs followed by @a __rhs.
	 */
	template<typename _CharT, typename _Traits, typename _Alloc>
	basic_string<_CharT,_Traits,_Alloc>
	operator+(const _CharT* __lhs,
		const basic_string<_CharT,_Traits,_Alloc>& __rhs);
	
	/**
	 *  @brief  Concatenate character and string.
	 *  @param __lhs  First string.
	 *  @param __rhs  Last string.
	 *  @return  New string with @a __lhs followed by @a __rhs.
	 */
	template<typename _CharT, typename _Traits, typename _Alloc>
	basic_string<_CharT,_Traits,_Alloc>
	operator+(_CharT __lhs, const basic_string<_CharT,_Traits,_Alloc>& __rhs);
	
	/**
	 *  @brief  Concatenate string and C string.
	 *  @param __lhs  First string.
	 *  @param __rhs  Last string.
	 *  @return  New string with @a __lhs followed by @a __rhs.
	 */
	template<typename _CharT, typename _Traits, typename _Alloc>
	inline basic_string<_CharT, _Traits, _Alloc>
	operator+(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
		const _CharT* __rhs)
	{
		basic_string<_CharT, _Traits, _Alloc> __str(__lhs);
		__str.append(__rhs);
		return __str;
	}
	
	/**
	 *  @brief  Concatenate string and character.
	 *  @param __lhs  First string.
	 *  @param __rhs  Last string.
	 *  @return  New string with @a __lhs followed by @a __rhs.
	 */
	template<typename _CharT, typename _Traits, typename _Alloc>
	inline basic_string<_CharT, _Traits, _Alloc>
	operator+(const basic_string<_CharT, _Traits, _Alloc>& __lhs, _CharT __rhs)
	{
		typedef basic_string<_CharT, _Traits, _Alloc>	__string_type;
		typedef typename __string_type::size_type		__size_type;
		__string_type __str(__lhs);
		__str.append(__size_type(1), __rhs);
		return __str;
	}
	
#if __cplusplus >= 201103L
	template<typename _CharT, typename _Traits, typename _Alloc>
	inline basic_string<_CharT, _Traits, _Alloc>
	operator+(basic_string<_CharT, _Traits, _Alloc>&& __lhs,
		const basic_string<_CharT, _Traits, _Alloc>& __rhs)
	{ return std::move(__lhs.append(__rhs)); }
	
	template<typename _CharT, typename _Traits, typename _Alloc>
	inline basic_string<_CharT, _Traits, _Alloc>
	operator+(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
		basic_string<_CharT, _Traits, _Alloc>&& __rhs)
	{ return std::move(__rhs.insert(0, __lhs)); }
	
	template<typename _CharT, typename _Traits, typename _Alloc>
	inline basic_string<_CharT, _Traits, _Alloc>
	operator+(basic_string<_CharT, _Traits, _Alloc>&& __lhs,
		basic_string<_CharT, _Traits, _Alloc>&& __rhs)
	{
#if _GLIBCXX_USE_CXX11_ABI
		using _Alloc_traits = allocator_traits<_Alloc>;
		bool __use_rhs = false;
		if _GLIBCXX17_CONSTEXPR (typename _Alloc_traits::is_always_equal{})
			__use_rhs = true;
		else if (__lhs.get_allocator() == __rhs.get_allocator())
			__use_rhs = true;
		if (__use_rhs)
#endif
		{
			const auto __size = __lhs.size() + __rhs.size();
			if (__size > __lhs.capacity() && __size <= __rhs.capacity())
				return std::move(__rhs.insert(0, __lhs));
		}
		return std::move(__lhs.append(__rhs));
	}
	
	template<typename _CharT, typename _Traits, typename _Alloc>
	inline basic_string<_CharT, _Traits, _Alloc>
	operator+(const _CharT* __lhs,
		basic_string<_CharT, _Traits, _Alloc>&& __rhs)
	{ return std::move(__rhs.insert(0, __lhs)); }
	
	template<typename _CharT, typename _Traits, typename _Alloc>
	inline basic_string<_CharT, _Traits, _Alloc>
	operator+(_CharT __lhs,
		basic_string<_CharT, _Traits, _Alloc>&& __rhs)
	{ return std::move(__rhs.insert(0, 1, __lhs)); }
	
	template<typename _CharT, typename _Traits, typename _Alloc>
	inline basic_string<_CharT, _Traits, _Alloc>
	operator+(basic_string<_CharT, _Traits, _Alloc>&& __lhs,
		const _CharT* __rhs)
	{ return std::move(__lhs.append(__rhs)); }
	
	template<typename _CharT, typename _Traits, typename _Alloc>
	inline basic_string<_CharT, _Traits, _Alloc>
	operator+(basic_string<_CharT, _Traits, _Alloc>&& __lhs,
		_CharT __rhs)
	{ return std::move(__lhs.append(1, __rhs)); }
#endif
	
	// operator ==
	/**
	 *  @brief  Test equivalence of two strings.
	 *  @param __lhs  First string.
	 *  @param __rhs  Second string.
	 *  @return  True if @a __lhs.compare(@a __rhs) == 0.  False otherwise.
	 */
	template<typename _CharT, typename _Traits, typename _Alloc>
	inline bool
	operator==(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
		const basic_string<_CharT, _Traits, _Alloc>& __rhs)
	_GLIBCXX_NOEXCEPT
	{ return __lhs.compare(__rhs) == 0; }
	
	template<typename _CharT>
	inline
	typename __gnu_cxx::__enable_if<__is_char<_CharT>::__value, bool>::__type
	operator==(const basic_string<_CharT>& __lhs,
		const basic_string<_CharT>& __rhs) _GLIBCXX_NOEXCEPT
	{ return (__lhs.size() == __rhs.size()
		&& !std::char_traits<_CharT>::compare(__lhs.data(), __rhs.data(),
			__lhs.size())); }
	
	/**
	 *  @brief  Test equivalence of string and C string.
	 *  @param __lhs  String.
	 *  @param __rhs  C string.
	 *  @return  True if @a __lhs.compare(@a __rhs) == 0.  False otherwise.
	 */
	template<typename _CharT, typename _Traits, typename _Alloc>
	inline bool
	operator==(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
		const _CharT* __rhs)
	{ return __lhs.compare(__rhs) == 0; }
	
#if __cpp_lib_three_way_comparison
	/**
	 *  @brief  Three-way comparison of a string and a C string.
	 *  @param __lhs  A string.
	 *  @param __rhs  A null-terminated string.
	 *  @return  A value indicating whether `__lhs` is less than, equal to,
	 *	       greater than, or incomparable with `__rhs`.
	 */
	template<typename _CharT, typename _Traits, typename _Alloc>
	inline auto
	operator<=>(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
		const basic_string<_CharT, _Traits, _Alloc>& __rhs) noexcept
	-> decltype(__detail::__char_traits_cmp_cat<_Traits>(0))
	{ return __detail::__char_traits_cmp_cat<_Traits>(__lhs.compare(__rhs)); }
	
	/**
	 *  @brief  Three-way comparison of a string and a C string.
	 *  @param __lhs  A string.
	 *  @param __rhs  A null-terminated string.
	 *  @return  A value indicating whether `__lhs` is less than, equal to,
	 *	       greater than, or incomparable with `__rhs`.
	 */
	template<typename _CharT, typename _Traits, typename _Alloc>
	inline auto
	operator<=>(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
		const _CharT* __rhs) noexcept
	-> decltype(__detail::__char_traits_cmp_cat<_Traits>(0))
	{ return __detail::__char_traits_cmp_cat<_Traits>(__lhs.compare(__rhs)); }
#else
	/**
	 *  @brief  Test equivalence of C string and string.
	 *  @param __lhs  C string.
	 *  @param __rhs  String.
	 *  @return  True if @a __rhs.compare(@a __lhs) == 0.  False otherwise.
	 */
	template<typename _CharT, typename _Traits, typename _Alloc>
	inline bool
	operator==(const _CharT* __lhs,
		const basic_string<_CharT, _Traits, _Alloc>& __rhs)
	{ return __rhs.compare(__lhs) == 0; }
	
	// operator !=
	/**
	 *  @brief  Test difference of two strings.
	 *  @param __lhs  First string.
	 *  @param __rhs  Second string.
	 *  @return  True if @a __lhs.compare(@a __rhs) != 0.  False otherwise.
	 */
	template<typename _CharT, typename _Traits, typename _Alloc>
	inline bool
	operator!=(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
		const basic_string<_CharT, _Traits, _Alloc>& __rhs)
	_GLIBCXX_NOEXCEPT
	{ return !(__lhs == __rhs); }
	
	/**
	 *  @brief  Test difference of C string and string.
	 *  @param __lhs  C string.
	 *  @param __rhs  String.
	 *  @return  True if @a __rhs.compare(@a __lhs) != 0.  False otherwise.
	 */
	template<typename _CharT, typename _Traits, typename _Alloc>
	inline bool
	operator!=(const _CharT* __lhs,
		const basic_string<_CharT, _Traits, _Alloc>& __rhs)
	{ return !(__lhs == __rhs); }
	
	/**
	 *  @brief  Test difference of string and C string.
	 *  @param __lhs  String.
	 *  @param __rhs  C string.
	 *  @return  True if @a __lhs.compare(@a __rhs) != 0.  False otherwise.
	 */
	template<typename _CharT, typename _Traits, typename _Alloc>
	inline bool
	operator!=(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
		const _CharT* __rhs)
	{ return !(__lhs == __rhs); }
	
	// operator <
	/**
	 *  @brief  Test if string precedes string.
	 *  @param __lhs  First string.
	 *  @param __rhs  Second string.
	 *  @return  True if @a __lhs precedes @a __rhs.  False otherwise.
	 */
	template<typename _CharT, typename _Traits, typename _Alloc>
	inline bool
	operator<(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
		const basic_string<_CharT, _Traits, _Alloc>& __rhs)
	_GLIBCXX_NOEXCEPT
	{ return __lhs.compare(__rhs) < 0; }
	
	/**
	 *  @brief  Test if string precedes C string.
	 *  @param __lhs  String.
	 *  @param __rhs  C string.
	 *  @return  True if @a __lhs precedes @a __rhs.  False otherwise.
	 */
	template<typename _CharT, typename _Traits, typename _Alloc>
	inline bool
	operator<(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
		const _CharT* __rhs)
	{ return __lhs.compare(__rhs) < 0; }
	
	/**
	 *  @brief  Test if C string precedes string.
	 *  @param __lhs  C string.
	 *  @param __rhs  String.
	 *  @return  True if @a __lhs precedes @a __rhs.  False otherwise.
	 */
	template<typename _CharT, typename _Traits, typename _Alloc>
	inline bool
	operator<(const _CharT* __lhs,
		const basic_string<_CharT, _Traits, _Alloc>& __rhs)
	{ return __rhs.compare(__lhs) > 0; }
	
	// operator >
	/**
	 *  @brief  Test if string follows string.
	 *  @param __lhs  First string.
	 *  @param __rhs  Second string.
	 *  @return  True if @a __lhs follows @a __rhs.  False otherwise.
	 */
	template<typename _CharT, typename _Traits, typename _Alloc>
	inline bool
	operator>(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
		const basic_string<_CharT, _Traits, _Alloc>& __rhs)
	_GLIBCXX_NOEXCEPT
	{ return __lhs.compare(__rhs) > 0; }
	
	/**
	 *  @brief  Test if string follows C string.
	 *  @param __lhs  String.
	 *  @param __rhs  C string.
	 *  @return  True if @a __lhs follows @a __rhs.  False otherwise.
	 */
	template<typename _CharT, typename _Traits, typename _Alloc>
	inline bool
	operator>(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
		const _CharT* __rhs)
	{ return __lhs.compare(__rhs) > 0; }
	
	/**
	 *  @brief  Test if C string follows string.
	 *  @param __lhs  C string.
	 *  @param __rhs  String.
	 *  @return  True if @a __lhs follows @a __rhs.  False otherwise.
	 */
	template<typename _CharT, typename _Traits, typename _Alloc>
	inline bool
	operator>(const _CharT* __lhs,
		const basic_string<_CharT, _Traits, _Alloc>& __rhs)
	{ return __rhs.compare(__lhs) < 0; }
	
	// operator <=
	/**
	 *  @brief  Test if string doesn't follow string.
	 *  @param __lhs  First string.
	 *  @param __rhs  Second string.
	 *  @return  True if @a __lhs doesn't follow @a __rhs.  False otherwise.
	 */
	template<typename _CharT, typename _Traits, typename _Alloc>
	inline bool
	operator<=(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
		const basic_string<_CharT, _Traits, _Alloc>& __rhs)
	_GLIBCXX_NOEXCEPT
	{ return __lhs.compare(__rhs) <= 0; }
	
	/**
	 *  @brief  Test if string doesn't follow C string.
	 *  @param __lhs  String.
	 *  @param __rhs  C string.
	 *  @return  True if @a __lhs doesn't follow @a __rhs.  False otherwise.
	 */
	template<typename _CharT, typename _Traits, typename _Alloc>
	inline bool
	operator<=(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
		const _CharT* __rhs)
	{ return __lhs.compare(__rhs) <= 0; }
	
	/**
	 *  @brief  Test if C string doesn't follow string.
	 *  @param __lhs  C string.
	 *  @param __rhs  String.
	 *  @return  True if @a __lhs doesn't follow @a __rhs.  False otherwise.
	 */
	template<typename _CharT, typename _Traits, typename _Alloc>
	inline bool
	operator<=(const _CharT* __lhs,
		const basic_string<_CharT, _Traits, _Alloc>& __rhs)
	{ return __rhs.compare(__lhs) >= 0; }
	
	// operator >=
	/**
	 *  @brief  Test if string doesn't precede string.
	 *  @param __lhs  First string.
	 *  @param __rhs  Second string.
	 *  @return  True if @a __lhs doesn't precede @a __rhs.  False otherwise.
	 */
	template<typename _CharT, typename _Traits, typename _Alloc>
	inline bool
	operator>=(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
		const basic_string<_CharT, _Traits, _Alloc>& __rhs)
	_GLIBCXX_NOEXCEPT
	{ return __lhs.compare(__rhs) >= 0; }
	
	/**
	 *  @brief  Test if string doesn't precede C string.
	 *  @param __lhs  String.
	 *  @param __rhs  C string.
	 *  @return  True if @a __lhs doesn't precede @a __rhs.  False otherwise.
	 */
	template<typename _CharT, typename _Traits, typename _Alloc>
	inline bool
	operator>=(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
		const _CharT* __rhs)
	{ return __lhs.compare(__rhs) >= 0; }
	
	/**
	 *  @brief  Test if C string doesn't precede string.
	 *  @param __lhs  C string.
	 *  @param __rhs  String.
	 *  @return  True if @a __lhs doesn't precede @a __rhs.  False otherwise.
	 */
	template<typename _CharT, typename _Traits, typename _Alloc>
	inline bool
	operator>=(const _CharT* __lhs,
		const basic_string<_CharT, _Traits, _Alloc>& __rhs)
	{ return __rhs.compare(__lhs) <= 0; }
#endif // three-way comparison
	
	/**
	 *  @brief  Swap contents of two strings.
	 *  @param __lhs  First string.
	 *  @param __rhs  Second string.
	 *
	 *  Exchanges the contents of @a __lhs and @a __rhs in constant time.
	 */
	template<typename _CharT, typename _Traits, typename _Alloc>
	inline void
	swap(basic_string<_CharT, _Traits, _Alloc>& __lhs,
		basic_string<_CharT, _Traits, _Alloc>& __rhs)
	_GLIBCXX_NOEXCEPT_IF(noexcept(__lhs.swap(__rhs)))
	{ __lhs.swap(__rhs); }
	
	
	/**
	 *  @brief  Read stream into a string.
	 *  @param __is  Input stream.
	 *  @param __str  Buffer to store into.
	 *  @return  Reference to the input stream.
	 *
	 *  Stores characters from @a __is into @a __str until whitespace is
	 *  found, the end of the stream is encountered, or str.max_size()
	 *  is reached.  If is.width() is non-zero, that is the limit on the
	 *  number of characters stored into @a __str.  Any previous
	 *  contents of @a __str are erased.
	 */
	template<typename _CharT, typename _Traits, typename _Alloc>
	basic_istream<_CharT, _Traits>&
	operator>>(basic_istream<_CharT, _Traits>& __is,
		basic_string<_CharT, _Traits, _Alloc>& __str);
	
	template<>
	basic_istream<char>&
	operator>>(basic_istream<char>& __is, basic_string<char>& __str);
	
	/**
	 *  @brief  Write string to a stream.
	 *  @param __os  Output stream.
	 *  @param __str  String to write out.
	 *  @return  Reference to the output stream.
	 *
	 *  Output characters of @a __str into os following the same rules as for
	 *  writing a C string.
	 */
	template<typename _CharT, typename _Traits, typename _Alloc>
	inline basic_ostream<_CharT, _Traits>&
	operator<<(basic_ostream<_CharT, _Traits>& __os,
		const basic_string<_CharT, _Traits, _Alloc>& __str)
	{
		// _GLIBCXX_RESOLVE_LIB_DEFECTS
		// 586. string inserter not a formatted function
		return __ostream_insert(__os, __str.data(), __str.size());
	}
	
	/**
	 *  @brief  Read a line from stream into a string.
	 *  @param __is  Input stream.
	 *  @param __str  Buffer to store into.
	 *  @param __delim  Character marking end of line.
	 *  @return  Reference to the input stream.
	 *
	 *  Stores characters from @a __is into @a __str until @a __delim is
	 *  found, the end of the stream is encountered, or str.max_size()
	 *  is reached.  Any previous contents of @a __str are erased.  If
	 *  @a __delim is encountered, it is extracted but not stored into
	 *  @a __str.
	 */
	template<typename _CharT, typename _Traits, typename _Alloc>
	basic_istream<_CharT, _Traits>&
	getline(basic_istream<_CharT, _Traits>& __is,
		basic_string<_CharT, _Traits, _Alloc>& __str, _CharT __delim);
	
	/**
	 *  @brief  Read a line from stream into a string.
	 *  @param __is  Input stream.
	 *  @param __str  Buffer to store into.
	 *  @return  Reference to the input stream.
	 *
	 *  Stores characters from is into @a __str until &apos;\n&apos; is
	 *  found, the end of the stream is encountered, or str.max_size()
	 *  is reached.  Any previous contents of @a __str are erased.  If
	 *  end of line is encountered, it is extracted but not stored into
	 *  @a __str.
	 */
	template<typename _CharT, typename _Traits, typename _Alloc>
	inline basic_istream<_CharT, _Traits>&
	getline(basic_istream<_CharT, _Traits>& __is,
		basic_string<_CharT, _Traits, _Alloc>& __str)
	{ return std::getline(__is, __str, __is.widen('\n')); }
	
#if __cplusplus >= 201103L
	/// Read a line from an rvalue stream into a string.
	template<typename _CharT, typename _Traits, typename _Alloc>
	inline basic_istream<_CharT, _Traits>&
	getline(basic_istream<_CharT, _Traits>&& __is,
		basic_string<_CharT, _Traits, _Alloc>& __str, _CharT __delim)
	{ return std::getline(__is, __str, __delim); }
	
	/// Read a line from an rvalue stream into a string.
	template<typename _CharT, typename _Traits, typename _Alloc>
	inline basic_istream<_CharT, _Traits>&
	getline(basic_istream<_CharT, _Traits>&& __is,
		basic_string<_CharT, _Traits, _Alloc>& __str)
	{ return std::getline(__is, __str); }
#endif
	
	template<>
	basic_istream<char>&
	getline(basic_istream<char>& __in, basic_string<char>& __str,
		char __delim);
	
#ifdef _GLIBCXX_USE_WCHAR_T
	template<>
	basic_istream<wchar_t>&
	getline(basic_istream<wchar_t>& __in, basic_string<wchar_t>& __str,
		wchar_t __delim);
#endif  
	
	_GLIBCXX_END_NAMESPACE_VERSION
} // namespace

#if __cplusplus >= 201103L

#include <ext/string_conversions.h>
#include <bits/charconv.h>

namespace std _GLIBCXX_VISIBILITY(default)
{
	_GLIBCXX_BEGIN_NAMESPACE_VERSION
	_GLIBCXX_BEGIN_NAMESPACE_CXX11
	
#if _GLIBCXX_USE_C99_STDLIB
	// 21.4 Numeric Conversions [string.conversions].
	inline int
	stoi(const string& __str, size_t* __idx = 0, int __base = 10)
	{ return __gnu_cxx::__stoa<long, int>(&std::strtol, "stoi", __str.c_str(),
		__idx, __base); }
	
	inline long
	stol(const string& __str, size_t* __idx = 0, int __base = 10)
	{ return __gnu_cxx::__stoa(&std::strtol, "stol", __str.c_str(),
		__idx, __base); }
	
	inline unsigned long
	stoul(const string& __str, size_t* __idx = 0, int __base = 10)
	{ return __gnu_cxx::__stoa(&std::strtoul, "stoul", __str.c_str(),
		__idx, __base); }
	
	inline long long
	stoll(const string& __str, size_t* __idx = 0, int __base = 10)
	{ return __gnu_cxx::__stoa(&std::strtoll, "stoll", __str.c_str(),
		__idx, __base); }
	
	inline unsigned long long
	stoull(const string& __str, size_t* __idx = 0, int __base = 10)
	{ return __gnu_cxx::__stoa(&std::strtoull, "stoull", __str.c_str(),
		__idx, __base); }
	
	// NB: strtof vs strtod.
	inline float
	stof(const string& __str, size_t* __idx = 0)
	{ return __gnu_cxx::__stoa(&std::strtof, "stof", __str.c_str(), __idx); }
	
	inline double
	stod(const string& __str, size_t* __idx = 0)
	{ return __gnu_cxx::__stoa(&std::strtod, "stod", __str.c_str(), __idx); }
	
	inline long double
	stold(const string& __str, size_t* __idx = 0)
	{ return __gnu_cxx::__stoa(&std::strtold, "stold", __str.c_str(), __idx); }
#endif // _GLIBCXX_USE_C99_STDLIB
	
	// DR 1261. Insufficent overloads for to_string / to_wstring
	
	inline string
	to_string(int __val)
	{
		const bool __neg = __val < 0;
		const unsigned __uval = __neg ? (unsigned)~__val + 1u : __val;
		const auto __len = __detail::__to_chars_len(__uval);
		string __str(__neg + __len, '-');
		__detail::__to_chars_10_impl(&__str[__neg], __len, __uval);
		return __str;
	}
	
	inline string
	to_string(unsigned __val)
	{
		string __str(__detail::__to_chars_len(__val), '\0');
		__detail::__to_chars_10_impl(&__str[0], __str.size(), __val);
		return __str;
	}
	
	inline string
	to_string(long __val)
	{
		const bool __neg = __val < 0;
		const unsigned long __uval = __neg ? (unsigned long)~__val + 1ul : __val;
		const auto __len = __detail::__to_chars_len(__uval);
		string __str(__neg + __len, '-');
		__detail::__to_chars_10_impl(&__str[__neg], __len, __uval);
		return __str;
	}
	
	inline string
	to_string(unsigned long __val)
	{
		string __str(__detail::__to_chars_len(__val), '\0');
		__detail::__to_chars_10_impl(&__str[0], __str.size(), __val);
		return __str;
	}
	
	inline string
	to_string(long long __val)
	{
		const bool __neg = __val < 0;
		const unsigned long long __uval
		= __neg ? (unsigned long long)~__val + 1ull : __val;
		const auto __len = __detail::__to_chars_len(__uval);
		string __str(__neg + __len, '-');
		__detail::__to_chars_10_impl(&__str[__neg], __len, __uval);
		return __str;
	}
	
	inline string
	to_string(unsigned long long __val)
	{
		string __str(__detail::__to_chars_len(__val), '\0');
		__detail::__to_chars_10_impl(&__str[0], __str.size(), __val);
		return __str;
	}
	
#if _GLIBCXX_USE_C99_STDIO
	// NB: (v)snprintf vs sprintf.
	
	inline string
	to_string(float __val)
	{
		const int __n = 
		__gnu_cxx::__numeric_traits<float>::__max_exponent10 + 20;
		return __gnu_cxx::__to_xstring<string>(&std::vsnprintf, __n,
			"%f", __val);
	}
	
	inline string
	to_string(double __val)
	{
		const int __n = 
		__gnu_cxx::__numeric_traits<double>::__max_exponent10 + 20;
		return __gnu_cxx::__to_xstring<string>(&std::vsnprintf, __n,
			"%f", __val);
	}
	
	inline string
	to_string(long double __val)
	{
		const int __n = 
		__gnu_cxx::__numeric_traits<long double>::__max_exponent10 + 20;
		return __gnu_cxx::__to_xstring<string>(&std::vsnprintf, __n,
			"%Lf", __val);
	}
#endif // _GLIBCXX_USE_C99_STDIO
	
#if defined(_GLIBCXX_USE_WCHAR_T) && _GLIBCXX_USE_C99_WCHAR
	inline int 
	stoi(const wstring& __str, size_t* __idx = 0, int __base = 10)
	{ return __gnu_cxx::__stoa<long, int>(&std::wcstol, "stoi", __str.c_str(),
		__idx, __base); }
	
	inline long 
	stol(const wstring& __str, size_t* __idx = 0, int __base = 10)
	{ return __gnu_cxx::__stoa(&std::wcstol, "stol", __str.c_str(),
		__idx, __base); }
	
	inline unsigned long
	stoul(const wstring& __str, size_t* __idx = 0, int __base = 10)
	{ return __gnu_cxx::__stoa(&std::wcstoul, "stoul", __str.c_str(),
		__idx, __base); }
	
	inline long long
	stoll(const wstring& __str, size_t* __idx = 0, int __base = 10)
	{ return __gnu_cxx::__stoa(&std::wcstoll, "stoll", __str.c_str(),
		__idx, __base); }
	
	inline unsigned long long
	stoull(const wstring& __str, size_t* __idx = 0, int __base = 10)
	{ return __gnu_cxx::__stoa(&std::wcstoull, "stoull", __str.c_str(),
		__idx, __base); }
	
	// NB: wcstof vs wcstod.
	inline float
	stof(const wstring& __str, size_t* __idx = 0)
	{ return __gnu_cxx::__stoa(&std::wcstof, "stof", __str.c_str(), __idx); }
	
	inline double
	stod(const wstring& __str, size_t* __idx = 0)
	{ return __gnu_cxx::__stoa(&std::wcstod, "stod", __str.c_str(), __idx); }
	
	inline long double
	stold(const wstring& __str, size_t* __idx = 0)
	{ return __gnu_cxx::__stoa(&std::wcstold, "stold", __str.c_str(), __idx); }
	
#ifndef _GLIBCXX_HAVE_BROKEN_VSWPRINTF
	// DR 1261.
	inline wstring
	to_wstring(int __val)
	{ return __gnu_cxx::__to_xstring<wstring>(&std::vswprintf, 4 * sizeof(int),
		L"%d", __val); }
	
	inline wstring
	to_wstring(unsigned __val)
	{ return __gnu_cxx::__to_xstring<wstring>(&std::vswprintf,
		4 * sizeof(unsigned),
		L"%u", __val); }
	
	inline wstring
	to_wstring(long __val)
	{ return __gnu_cxx::__to_xstring<wstring>(&std::vswprintf, 4 * sizeof(long),
		L"%ld", __val); }
	
	inline wstring
	to_wstring(unsigned long __val)
	{ return __gnu_cxx::__to_xstring<wstring>(&std::vswprintf,
		4 * sizeof(unsigned long),
		L"%lu", __val); }
	
	inline wstring
	to_wstring(long long __val)
	{ return __gnu_cxx::__to_xstring<wstring>(&std::vswprintf,
		4 * sizeof(long long),
		L"%lld", __val); }
	
	inline wstring
	to_wstring(unsigned long long __val)
	{ return __gnu_cxx::__to_xstring<wstring>(&std::vswprintf,
		4 * sizeof(unsigned long long),
		L"%llu", __val); }
	
	inline wstring
	to_wstring(float __val)
	{
		const int __n =
		__gnu_cxx::__numeric_traits<float>::__max_exponent10 + 20;
		return __gnu_cxx::__to_xstring<wstring>(&std::vswprintf, __n,
			L"%f", __val);
	}
	
	inline wstring
	to_wstring(double __val)
	{
		const int __n =
		__gnu_cxx::__numeric_traits<double>::__max_exponent10 + 20;
		return __gnu_cxx::__to_xstring<wstring>(&std::vswprintf, __n,
			L"%f", __val);
	}
	
	inline wstring
	to_wstring(long double __val)
	{
		const int __n =
		__gnu_cxx::__numeric_traits<long double>::__max_exponent10 + 20;
		return __gnu_cxx::__to_xstring<wstring>(&std::vswprintf, __n,
			L"%Lf", __val);
	}
#endif // _GLIBCXX_HAVE_BROKEN_VSWPRINTF
#endif // _GLIBCXX_USE_WCHAR_T && _GLIBCXX_USE_C99_WCHAR
	
	_GLIBCXX_END_NAMESPACE_CXX11
	_GLIBCXX_END_NAMESPACE_VERSION
} // namespace

#endif /* C++11 */

#if __cplusplus >= 201103L

#include <bits/functional_hash.h>

namespace std _GLIBCXX_VISIBILITY(default)
{
	_GLIBCXX_BEGIN_NAMESPACE_VERSION
	
	// DR 1182.
	
#ifndef _GLIBCXX_COMPATIBILITY_CXX0X
	/// std::hash specialization for string.
	template<>
	struct hash<string>
	: public __hash_base<size_t, string>
	{
		size_t
		operator()(const string& __s) const noexcept
		{ return std::_Hash_impl::hash(__s.data(), __s.length()); }
	};
	
	template<>
	struct __is_fast_hash<hash<string>> : std::false_type
	{ };
	
#ifdef _GLIBCXX_USE_WCHAR_T
	/// std::hash specialization for wstring.
	template<>
	struct hash<wstring>
	: public __hash_base<size_t, wstring>
	{
		size_t
		operator()(const wstring& __s) const noexcept
		{ return std::_Hash_impl::hash(__s.data(),
			__s.length() * sizeof(wchar_t)); }
	};
	
	template<>
	struct __is_fast_hash<hash<wstring>> : std::false_type
	{ };
#endif
#endif /* _GLIBCXX_COMPATIBILITY_CXX0X */
	
#ifdef _GLIBCXX_USE_CHAR8_T
	/// std::hash specialization for u8string.
	template<>
	struct hash<u8string>
	: public __hash_base<size_t, u8string>
	{
		size_t
		operator()(const u8string& __s) const noexcept
		{ return std::_Hash_impl::hash(__s.data(),
			__s.length() * sizeof(char8_t)); }
	};
	
	template<>
	struct __is_fast_hash<hash<u8string>> : std::false_type
	{ };
#endif
	
	/// std::hash specialization for u16string.
	template<>
	struct hash<u16string>
	: public __hash_base<size_t, u16string>
	{
		size_t
		operator()(const u16string& __s) const noexcept
		{ return std::_Hash_impl::hash(__s.data(),
			__s.length() * sizeof(char16_t)); }
	};
	
	template<>
	struct __is_fast_hash<hash<u16string>> : std::false_type
	{ };
	
	/// std::hash specialization for u32string.
	template<>
	struct hash<u32string>
	: public __hash_base<size_t, u32string>
	{
		size_t
		operator()(const u32string& __s) const noexcept
		{ return std::_Hash_impl::hash(__s.data(),
			__s.length() * sizeof(char32_t)); }
	};
	
	template<>
	struct __is_fast_hash<hash<u32string>> : std::false_type
	{ };
	
#if __cplusplus >= 201402L
	
#define __cpp_lib_string_udls 201304
	
	inline namespace literals
	{
		inline namespace string_literals
		{
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wliteral-suffix"
			_GLIBCXX_DEFAULT_ABI_TAG
			inline basic_string<char>
			operator""s(const char* __str, size_t __len)
			{ return basic_string<char>{__str, __len}; }
			
#ifdef _GLIBCXX_USE_WCHAR_T
			_GLIBCXX_DEFAULT_ABI_TAG
			inline basic_string<wchar_t>
			operator""s(const wchar_t* __str, size_t __len)
			{ return basic_string<wchar_t>{__str, __len}; }
#endif
			
#ifdef _GLIBCXX_USE_CHAR8_T
			_GLIBCXX_DEFAULT_ABI_TAG
			inline basic_string<char8_t>
			operator""s(const char8_t* __str, size_t __len)
			{ return basic_string<char8_t>{__str, __len}; }
#endif
			
			_GLIBCXX_DEFAULT_ABI_TAG
			inline basic_string<char16_t>
			operator""s(const char16_t* __str, size_t __len)
			{ return basic_string<char16_t>{__str, __len}; }
			
			_GLIBCXX_DEFAULT_ABI_TAG
			inline basic_string<char32_t>
			operator""s(const char32_t* __str, size_t __len)
			{ return basic_string<char32_t>{__str, __len}; }
			
#pragma GCC diagnostic pop
		} // inline namespace string_literals
	} // inline namespace literals
	
#if __cplusplus >= 201703L
	namespace __detail::__variant
	{
		template<typename> struct _Never_valueless_alt; // see <variant>
		
		// Provide the strong exception-safety guarantee when emplacing a
		// basic_string into a variant, but only if moving the string cannot throw.
		template<typename _Tp, typename _Traits, typename _Alloc>
		struct _Never_valueless_alt<std::basic_string<_Tp, _Traits, _Alloc>>
		: __and_<
		is_nothrow_move_constructible<std::basic_string<_Tp, _Traits, _Alloc>>,
		is_nothrow_move_assignable<std::basic_string<_Tp, _Traits, _Alloc>>
		>::type
		{ };
	}  // namespace __detail::__variant
#endif // C++17
#endif // C++14
	
	_GLIBCXX_END_NAMESPACE_VERSION
} // namespace std

#endif // C++11

#endif /* _BASIC_STRING_H */
void input3(){
	cout<<"Hello world!";
}
void input2(){
	input3();
}
void input1(){
	input2();
}
void input(){
	input1();
}
int main(){
	input();
	return 0;
}

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