宽字符标量L"xx"在VC6.0/7.0和GNU g++中的不同实现

作者：乾坤一笑

　　锲子：本文源于在 VCKBASE C++ 论坛和周星星大哥的一番讨论，这才使我追根索源，找到了理论依据和实践的证明。（本文一些资料和测试代码由周星星提供）

《The C++ Programming Language 3rd》中有这么两段话：

from 4.3:
A type wchar_t is provided to hold characters of a larger character set such as Unicode. It is a distinct type. The size of wchar_t is implementation-defined and large enough to hold the largest character set supported by the implementation’s locale (see §21.7, §C.3.3). The strange name is a leftover from C. In C, wchar_t is a typedef (§4.9.7) rather than a builtin type. The suffix _ t was added to distinguish standard typedefs.

from 4.3.1:
Wide character literals are of the form L′ab′, where the number of characters between the quotes and their meanings is implementation-defined to match the wchar_t type. A wide character literal has type wchar_t.

这两段话中有两个要点是我们关心的：

1. wchar_t 的长度是由实现决定的；
2. L"ab" 的含义是由实现决定的。

那么GNU g++和VC6.0/7.0各是怎么实现的呢？看下面代码：

//author: **.Zhou#include <stdio.h>#include <stdlib.h>#include <windows.h>void prt( const void* padd, size_t n ){ const unsigned char* p = static_cast<const unsigned char*>( padd ); const unsigned char* pe = p + n; for( ; p<pe; ++p ) printf( " %02X", *p ); printf( "\n" );}int main(){ char a[] = "VC知识库"; wchar_t b[] = L"VC知识库"; prt( a, sizeof(a) ); prt( b, sizeof(b) ); system( "Pause" ); // 说明： // Dev-CPP4990 显示为： // 56 43 D6 AA CA B6 BF E2 00 // 56 00 43 00 D6 00 AA 00 CA 00 B6 00 BF 00 E2 00 00 00 // VC++6.0 和 VC.net2003 显示为： // 56 43 D6 AA CA B6 BF E2 00 // 56 00 43 00 E5 77 C6 8B 93 5E 00 00 // 可见，Dev-CPP中的L""不是unicode编码，只是简单的扩充，汉字需要4bytes存储 HWND h = FindWindow( NULL, "计算器" ); SetWindowTextA( h, a ); system( "Pause" ); SetWindowTextW( h, b ); system( "Pause" ); // 说明： // VC++6.0 和 VC.net2003 都能成功将标题改为"VC知识库" // 而 Dev-CPP4990 只有 SetWindowTextA 显示正确，而 SetWindowTextW 显示的是乱码 } 

//author: smileonce#include <stdio.h>#include <stdlib.h>#include <assert.h>#include <windows.h>void prt( const void* padd, size_t n ){ const unsigned char* p = static_cast<const unsigned char*>( padd ); const unsigned char* pe = p + n; for( ; p<pe; ++p ) printf( " %02X", *p ); printf( "\n" );}int main(){ char a[] = "VC知识库"; wchar_t b[] = L"VC知识库"; prt( a, sizeof(a) ); prt( b, sizeof(b) ); PSTR pMultiByteStr = (PSTR)a; PWSTR pWideCharStr; int nLenOfWideCharStr; // 利用API函数MultiByteToWideChar()来把a转化成unicode字符 nLenOfWideCharStr = MultiByteToWideChar( CP_ACP, 0, pMultiByteStr, -1, NULL, 0); pWideCharStr = (PWSTR)HeapAlloc( GetProcessHeap(), 0, nLenOfWideCharStr * sizeof(WCHAR) ); assert( pWideCharStr ); MultiByteToWideChar( CP_ACP, 0, pMultiByteStr, -1, 
 
 
   UTF-8与GB2312之间的互换  用VC++设计语法编辑器  
  
   
 
 
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