C++ map.insert: pair和make_pair区别

本文详细解析了C++中map容器的插入操作,对比了直接赋值、使用pair构造函数及make_pair的不同之处,并解释了这些方法在实际应用中的优缺点。
 1 C++ map.insert: pair和make_pair区别
 2 \*********************************\
 3     map<uint32_t, string> temp;
 4     1. temp[1] = "template";
 5     2.temp.insert(pair<uint32_t, string>(1, "template"));
 6     3.temp.insert(make_pair(1, "template"));
 7 
 8     pair实质上是一个结构体,其主要的两个成员变量是first和second,因此有了 
    for(const auto& i : temp) { 9 cout << "first = " << i.first; // i 也就是一个pair; 10 cout << "second = " << i.second; 11 } 12 pair需要指定构造的类型,make_pair可以隐式转换,即将1 转成uint32_t, template转成string类型。 13 \*********************************\

 

转载于:https://www.cnblogs.com/kilen/p/9242581.html

In file included from D:/SelfUsing/Language/CLion 2025.1.3/mingw/lib/gcc/x86_64-w64-mingw32/14.2.0/include/c++/bits/hashtable_policy.h:34, from D:/SelfUsing/Language/CLion 2025.1.3/mingw/lib/gcc/x86_64-w64-mingw32/14.2.0/include/c++/bits/hashtable.h:35, from D:/SelfUsing/Language/CLion 2025.1.3/mingw/lib/gcc/x86_64-w64-mingw32/14.2.0/include/c++/bits/unordered_map.h:33, from D:/SelfUsing/Language/CLion 2025.1.3/mingw/lib/gcc/x86_64-w64-mingw32/14.2.0/include/c++/unordered_map:41, from D:/obj/i wanna own world to me/i wanna own world to me.cpp:9: D:/SelfUsing/Language/CLion 2025.1.3/mingw/lib/gcc/x86_64-w64-mingw32/14.2.0/include/c++/tuple: In instantiation of 'constexpr std::pair<_T1, _T2>::pair(std::tuple<_Args1 ...>&, std::tuple<_Args2 ...>&, std::_Index_tuple<_Indexes1 ...>, std::_Index_tuple<_Indexes2 ...>) [with _Args1 = {std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >&&}; long long unsigned int ..._Indexes1 = {0}; _Args2 = {}; long long unsigned int ..._Indexes2 = {}; _T1 = const std::__cxx11::basic_string<char>; _T2 = SDL_GL_Image]': D:/SelfUsing/Language/CLion 2025.1.3/mingw/lib/gcc/x86_64-w64-mingw32/14.2.0/include/c++/tuple:2877:63: required from 'constexpr std::pair<_T1, _T2>::pair(std::piecewise_construct_t, std::tuple<_Args1 ...>, std::tuple<_Args2 ...>) [with _Args1 = {std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >&&}; _Args2 = {}; _T1 = const std::__cxx11::basic_string<char>; _T2 = SDL_GL_Image]' 2877 | typename _Build_index_tuple<sizeof...(_Args2)>::__type()) | ^ D:/SelfUsing/Language/CLion 2025.1.3/mingw/lib/gcc/x86_64-w64-mingw32/14.2.0/include/c++/bits/stl_construct.h:97:14: required from 'constexpr decltype (::new(void*(0)) _Tp) std::construct_at(_Tp*, _Args&& ...) [with _Tp = pair<const __cxx11::basic_string<char>, SDL_GL_Image>; _Args = {const piecewise_construct_t&, tuple<__cxx11::basic_string<char, char_traits<char>, allocator<char> >&&>, tuple<>}; decltype (::new(void*(0)) _Tp) = pair<const __cxx11::basic_string<char>, SDL_GL_Image>*]' 97 | { return ::new((void*)__location) _Tp(std::forward<_Args>(__args)...); } | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ D:/SelfUsing/Language/CLion 2025.1.3/mingw/lib/gcc/x86_64-w64-mingw32/14.2.0/include/c++/bits/alloc_traits.h:536:21: required from 'static constexpr void std::allocator_traits<std::allocator<_Up> >::construct(allocator_type&, _Up*, _Args&& ...) [with _Up = std::pair<const std::__cxx11::basic_string<char>, SDL_GL_Image>; _Args = {const std::piecewise_construct_t&, std::tuple<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >&&>, std::tuple<>}; _Tp = std::__detail::_Hash_node<std::pair<const std::__cxx11::basic_string<char>, SDL_GL_Image>, true>; allocator_type = std::allocator<std::__detail::_Hash_node<std::pair<const std::__cxx11::basic_string<char>, SDL_GL_Image>, true> >]' 536 | std::construct_at(__p, std::forward<_Args>(__args)...); | ~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ D:/SelfUsing/Language/CLion 2025.1.3/mingw/lib/gcc/x86_64-w64-mingw32/14.2.0/include/c++/bits/hashtable_policy.h:2024:36: required from 'std::__detail::_Hashtable_alloc<_NodeAlloc>::__node_type* std::__detail::_Hashtable_alloc<_NodeAlloc>::_M_allocate_node(_Args&& ...) [with _Args = {const std::piecewise_construct_t&, std::tuple<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >&&>, std::tuple<>}; _NodeAlloc = std::allocator<std::__detail::_Hash_node<std::pair<const std::__cxx11::basic_string<char>, SDL_GL_Image>, true> >; __node_ptr = std::allocator<std::__detail::_Hash_node<std::pair<const std::__cxx11::basic_string<char>, SDL_GL_Image>, true> >::value_type*]' 2024 | __node_alloc_traits::construct(__alloc, __n->_M_valptr(), | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~ 2025 | std::forward<_Args>(__args)...); | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ D:/SelfUsing/Language/CLion 2025.1.3/mingw/lib/gcc/x86_64-w64-mingw32/14.2.0/include/c++/bits/hashtable.h:312:35: required from 'std::_Hashtable<_Key, _Value, _Alloc, _ExtractKey, _Equal, _Hash, _RangeHash, _Unused, _RehashPolicy, _Traits>::_Scoped_node::_Scoped_node(std::_Hashtable<_Key, _Value, _Alloc, _ExtractKey, _Equal, _Hash, _RangeHash, _Unused, _RehashPolicy, _Traits>::__hashtable_alloc*, _Args&& ...) [with _Args = {const std::piecewise_construct_t&, std::tuple<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >&&>, std::tuple<>}; _Key = std::__cxx11::basic_string<char>; _Value = std::pair<const std::__cxx11::basic_string<char>, SDL_GL_Image>; _Alloc = std::allocator<std::pair<const std::__cxx11::basic_string<char>, SDL_GL_Image> >; _ExtractKey = std::__detail::_Select1st; _Equal = std::equal_to<std::__cxx11::basic_string<char> >; _Hash = std::hash<std::__cxx11::basic_string<char> >; _RangeHash = std::__detail::_Mod_range_hashing; _Unused = std::__detail::_Default_ranged_hash; _RehashPolicy = std::__detail::_Prime_rehash_policy; _Traits = std::__detail::_Hashtable_traits<true, false, true>; std::_Hashtable<_Key, _Value, _Alloc, _ExtractKey, _Equal, _Hash, _RangeHash, _Unused, _RehashPolicy, _Traits>::__hashtable_alloc = std::_Hashtable<std::__cxx11::basic_string<char>, std::pair<const std::__cxx11::basic_string<char>, SDL_GL_Image>, std::allocator<std::pair<const std::__cxx11::basic_string<char>, SDL_GL_Image> >, std::__detail::_Select1st, std::equal_to<std::__cxx11::basic_string<char> >, std::hash<std::__cxx11::basic_string<char> >, std::__detail::_Mod_range_hashing, std::__detail::_Default_ranged_hash, std::__detail::_Prime_rehash_policy, std::__detail::_Hashtable_traits<true, false, true> >::__hashtable_alloc]' 312 | _M_node(__h->_M_allocate_node(std::forward<_Args>(__args)...)) | ~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ D:/SelfUsing/Language/CLion 2025.1.3/mingw/lib/gcc/x86_64-w64-mingw32/14.2.0/include/c++/bits/hashtable_policy.h:870:42: required from 'std::__detail::_Map_base<_Key, std::pair<const _Key, _Val>, _Alloc, std::__detail::_Select1st, _Equal, _Hash, _RangeHash, _Unused, _RehashPolicy, _Traits, true>::mapped_type& std::__detail::_Map_base<_Key, std::pair<const _Key, _Val>, _Alloc, std::__detail::_Select1st, _Equal, _Hash, _RangeHash, _Unused, _RehashPolicy, _Traits, true>::operator[](key_type&&) [with _Key = std::__cxx11::basic_string<char>; _Val = SDL_GL_Image; _Alloc = std::allocator<std::pair<const std::__cxx11::basic_string<char>, SDL_GL_Image> >; _Equal = std::equal_to<std::__cxx11::basic_string<char> >; _Hash = std::hash<std::__cxx11::basic_string<char> >; _RangeHash = std::__detail::_Mod_range_hashing; _Unused = std::__detail::_Default_ranged_hash; _RehashPolicy = std::__detail::_Prime_rehash_policy; _Traits = std::__detail::_Hashtable_traits<true, false, true>; mapped_type = SDL_GL_Image; key_type = std::__cxx11::basic_string<char>]' 870 | typename __hashtable::_Scoped_node __node { | ^~~~~~ D:/SelfUsing/Language/CLion 2025.1.3/mingw/lib/gcc/x86_64-w64-mingw32/14.2.0/include/c++/bits/unordered_map.h:992:20: required from 'std::unordered_map<_Key, _Tp, _Hash, _Pred, _Alloc>::mapped_type& std::unordered_map<_Key, _Tp, _Hash, _Pred, _Alloc>::operator[](key_type&&) [with _Key = std::__cxx11::basic_string<char>; _Tp = SDL_GL_Image; _Hash = std::hash<std::__cxx11::basic_string<char> >; _Pred = std::equal_to<std::__cxx11::basic_string<char> >; _Alloc = std::allocator<std::pair<const std::__cxx11::basic_string<char>, SDL_GL_Image> >; mapped_type = SDL_GL_Image; key_type = std::__cxx11::basic_string<char>]' 992 | { return _M_h[std::move(__k)]; } | ~~~~^ D:/obj/i wanna own world to me/i wanna own world to me.cpp:164:57: required from here 164 | glBindTexture(GL_TEXTURE_2D, images["sprBrownBlock"s].textureID); | ^ D:/SelfUsing/Language/CLion 2025.1.3/mingw/lib/gcc/x86_64-w64-mingw32/14.2.0/include/c++/tuple:2888:9: error: no matching function for call to 'SDL_GL_Image::SDL_GL_Image()' 2888 | second(std::forward<_Args2>(std::get<_Indexes2>(__tuple2))...) | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ D:/obj/i wanna own world to me/i wanna own world to me.cpp:43:14: note: candidate: 'SDL_GL_Image::SDL_GL_Image(const char*)' 43 | explicit SDL_GL_Image(const char* path) { | ^~~~~~~~~~~~ D:/obj/i wanna own world to me/i wanna own world to me.cpp:43:14: note: candidate expects 1 argument, 0 provided D:/obj/i wanna own world to me/i wanna own world to me.cpp:39:7: note: candidate: 'constexpr SDL_GL_Image::SDL_GL_Image(const SDL_GL_Image&)' 39 | union SDL_GL_Image { | ^~~~~~~~~~~~ D:/obj/i wanna own world to me/i wanna own world to me.cpp:39:7: note: candidate expects 1 argument, 0 provided ninja: build stopped: subcommand failed.
08-05
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