char*， wchat_t*互转 及 A2T, T2A宏及其实现原理

本文的内容是在 上一篇博文 ASCI, GB2312, UNICODE, UTF8编码比较 的基础上的。

char :单字节变量类型，表示ASCII码。

wchar_t :宽字节变量类型，用于表示Unicode字符。在<string.h>定义为：typedef unsigned short wchar_t。

TCHAR: VS下的中间类型。在“使用Unicode字符集”下TCHAR定义为wchar_t，在字符集 “未设置” 条件下TCHAR定义为char。

A2T，及T2A是两个非常有用的宏，可以用于实现char*和wchar_t*字符串之间的转换。宏的实现也将会在测试代码中给出，不感兴趣的直接跳过。费话不多说，直接上测试代码，参考代码注释。

// demo1.cpp : 定义控制台应用程序的入口点。//#include "stdafx.h"#include <iostream>#include <cstring>using namespace std;#include <atlbase.h>#include <Windows.h>void test_L_macro(){ char astr[] = "hello";cout<<"sizeof(astr):"<<sizeof(astr)<<endl<<"strlen(astr):"<<strlen(astr)<<endl;//L"str"表示将ANSI字符串转换成unicode的字符串，就是每个字符占用两个字节。wchar_t wstr[] = L"hello"; //typedef unsigned short wchar_tcout<<"sizeof(wstr)"<<sizeof(wstr)<<endl<<"wcslen(wstr):"<<wcslen(wstr)<<endl;}void test_T_macro(){/*#ifdef   _UNICODE#define __T(x)      L ## x#else#define __T(x)      x#endif#define _T(x)       __T(x)#define _TEXT(x)    __T(x)#define TEXT(quote) __TEXT(quote)#ifdef _UNICODE   typedef char TCHAR;   #else   typede wchar_t TCHAR;   #endif *///如果在程序中使用了TCHAR，那么就不应该使用ANSI的strXXX函数或者Unicode的wcsXXX函数了，//而必须使用tchar.h中定义的_tcsXXX函数。TCHAR buf[] = _T("hello");cout<<"sizeof(buf):"<<sizeof(buf)<<endl<<"_tcslen(lpBuf):"<<_tcslen(buf)<<endl; /*#ifdef _UNICODE   typedef wchar_t WCHAR;// wc,   16-bit UNICODE charactertypedef __nullterminated WCHAR *LPWSTR;typedef LPWSTR PTSTR, LPTSTR;#else   typedef char CHAR;typedef __nullterminated CHAR *LPSTR;typedef LPSTR LPTSTR;#endif */LPTSTR lpBuf = TEXT("hello");cout<<"_tcslen(lpBuf):"<<_tcslen(lpBuf)<<endl;  }void test_A2T(){USES_CONVERSION;char *astr = "hello";LPTSTR wstr = A2T(astr);#ifdef _UNICODEwcout<<"wcout\<\<wstr:"<<wstr<<endl;#elsecout<<"cout\<\<wstr:"<<wstr<<endl;#endif}void test_A2T_(){int _convert = 0;(_convert); UINT _acp = ATL::_AtlGetConversionACP() ; (_acp); LPCWSTR _lpw = 0; (_lpw); LPCSTR _lpa = 0; (_lpa);char *astr = "hello";LPTSTR wstr = ( ((_lpa = astr) == 0) ? 0 : ( _convert = (lstrlenA(_lpa)+1), (2147483647/2<_convert)? 0 : AtlA2WHelper((LPWSTR) _alloca(_convert*sizeof(WCHAR)), _lpa, _convert, _acp)));//p.s. AtlA2WHelper调用了函数MultiByteToWideChar//_alloca函数用于在栈上分配内存，参考：http://msdn.microsoft.com/en-us/library/wb1s57t5.aspxwcout<<"wcout\<\<wstr:"<<wstr<<endl;}void test_T2A(){USES_CONVERSION;LPTSTR wstr = _T("hello");char *astr = T2A(wstr);cout<<"cout\<\<astr:"<<astr<<endl;}void test_T2A_(){int _convert = 0; (_convert); UINT _acp = ATL::_AtlGetConversionACP() ; (_acp); LPCWSTR _lpw = 0; (_lpw); LPCSTR _lpa = 0; (_lpa);LPTSTR wstr = L"hello";char *astr = ( ((_lpw = wstr) == 0) ? 0 : ( (_convert = (lstrlenW(_lpw)+1), (_convert>2147483647/2) ? 0 : AtlW2AHelper((LPSTR) _alloca(_convert*sizeof(WCHAR)), _lpw, _convert*sizeof(WCHAR), _acp))));//p.s. AtlW2AHelper调用了函数WideCharToMultiByte//_alloca函数用于在栈上分配内存，参考：http://msdn.microsoft.com/en-us/library/wb1s57t5.aspxcout<<"cout\<\<astr:"<<astr<<endl;}int main(){test_L_macro();test_T_macro();test_A2T();test_A2T_();test_T2A();test_T2A_();}

P.S.

test_A2T_ 是 test_A2T的宏替换实现；test_T2A_ 是 test_T2A的宏替换实现；