SDL入门教程(九):4、int转换为std::string

本文介绍了一种在SDL环境中将整型数字转换为字符串的方法。该方法首先判断数字是否为负,接着计算数字的位数,再逐位读取数字并将其添加到字符串中。文章还提供了一个具体的实现示例。

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作者:龙飞

        我下面考虑的问题,是用TextSurface反馈鼠标事件的信息。我想到的第一个例子,很自然就是反馈鼠标所在坐标的位置。这里涉及到一个基础的问题,即鼠标位置显然不是用字符串表示的。SDL给我们的反馈信息是int,我们需要用TextSurface将int构建成可以被blit到ScreenSurface上的面,需要做的第一件事情,是将int转换为string。
        我的思路是这样的:首先找到int的数位数;然后依次从高位读取数字,之后将这个位去掉(通常减掉是最简单的);依次记录这些数字,转换成string,然后将这些数字“加”(字符串的合并)起来。
头文件如下:
//UVi Soft (2008)
//Long Fei (lf426), E-mail: zbln426@163.com

//FileName: int_to_string.h

#ifndef INT_TO_STRING_H_
#define INT_TO_STRING_H_

#include 
<iostream>
#include 
<string>
#include 
<vector>

int int_power(int baseint exp);
std::
string int_to_string(int num);

#endif
        其中,int_to_string()是我们需要构建的函数,int_power()是求一个数的整数幂的函数。这么简单的算法,我们就自己写吧。至于用到vector,按照我的思路,我们需要的数据结构显然应该是“队列”(先进先出)。不过真得感谢STL,用vector显然不是最优化的,但是肯定是最“通俗”的,因为即使是作为非专业的队列(或者栈),vector也已经为我们提供了必要的方法,比如推入(push_back)。
        下面我就把程序说明夹在程序中间了。原因是本人英语太菜,简单描述还能忍,描述算法就有点不能忍了-_-!!!。另外,尽管我英语这水平,我还是希望程序里面别用中文注释的好。这种事情,您见过一次乱码,就总是得恶心一辈子。
//UVi Soft (2008)
//Long Fei (lf426), E-mail: zbln426@163.com

#include 
"int_to_string.h"

int int_power(int baseint exp)
{
    
int result = 1;
    
for (int i = exp; i > 0; i-- )
        result
*=base;
    
return result;
}
这是个很简单的求幂的算法。其实我们在程序中,只需要用到求10的n次幂,所以,实际上我们还可以写得更加有针对一点。
std::string int_to_string(int num)
{
    
bool negative = false;
    
if ( num < 0 ){
        negative 
= true;
        num 
= -num;
    }
这开始写转换函数了。首先我们判定int是否为负。如果是,我们把它变成其相反数,然后与正数一样转换,最后在前面加上“-”就OK了。
    int bitNum = 1;
    
for ( int i = num; i > 9; i/=10 )
        bitNum
++;
bitNum是这个int的数位数。比如3就是1位,1024就是4位。
    std::vector<int> eachNum;
    
for ( int i = bitNum, temp = num; i > 0; i-- ){
        
int highBit = int(temp/int_power(10, (i-1)));
        eachNum.push_back(highBit);
        temp
-=(highBit*int_power(10, (i-1)));
    }
我们通过vector数组纪录每个数位上的数字,从高位到低位。需要说明的是,n位的数字是10的n-1次方幂。比如1024是4位,而1000是10的3次方幂。所以,我们这里用的是i-1而非i。
    std::string str;
    
if ( negative == true )
        str 
= "-";
    
for ( std::vector<int>::iterator pTemp = eachNum.begin(); pTemp != eachNum.end(); pTemp++ ){
        
switch ( *pTemp ){
            
case 0:
                str
+="0";
                
break;
            
case 1:
                str
+="1";
                
break;
            
case 2:
                str
+="2";
                
break;
            
case 3:
                str
+="3";
                
break;
            
case 4:
                str
+="4";
                
break;
            
case 5:
                str
+="5";
                
break;
            
case 6:
                str
+="6";
                
break;
            
case 7:
                str
+="7";
                
break;
            
case 8:
                str
+="8";
                
break;
            
case 9:
                str
+="9";
                
break;
            
default:
                
break;
        }
    }
    
return str;
}
最后,我们用了STL的方法将每个数字转换成std::string的字符串,然后将这些字符串合并起来,作为函数的返回值。
        我们在下一节中将用TextSurface演示这个函数的作用,以及实现我们在本节前面所提出的问题。  
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.
最新发布
08-05
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