宽字符标量L"xx"在VC6.0/7.0和GNU g++中的不同实现

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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：

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.hvoid 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.hvoid 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,