"_T"有什么用?怎么使用？

是一个宏，比如CString str=_T("Test");如果定义了UNICODE（#define UNICODE);
则str的内容是unicode的“Test”（每个字母占两个字节），否则就是ansi的“Test”(每个字母占一个字节).
A Sample Generic-Text Program
Microsoft Specific —>The following program, GENTEXT.C, provides a more detailed illustration of the use of generic-text mappings defined in TCHAR.H:/*
* GENTEXT.C: use of generic-text mappings defined in TCHAR.H
*            Generic-Text-Mapping example program
*/#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <direct.h>
#include <errno.h>
#include <tchar.h>int __cdecl _tmain(int argc, _TCHAR **argv, _TCHAR **envp)
{
   _TCHAR buff[_MAX_PATH];
   _TCHAR *str = _T("Astring");
   char *amsg = "Reversed";
   wchar_t *wmsg = L"Is";#ifdef _UNICODE
   printf("Unicode version\n");
#else /* _UNICODE */
#ifdef _MBCS
   printf("MBCS version\n");
#else
   printf("SBCS version\n");
#endif
#endif /* _UNICODE */   if (_tgetcwd(buff, _MAX_PATH) == NULL)
       printf("Can't Get Current Directory - errno=%d\n", errno);
   else
       _tprintf(_T("Current Directory is '%s'\n"), buff);
   _tprintf(_T("'%s' %hs %ls:\n"), str, amsg, wmsg);
   _tprintf(_T("'%s'\n"), _tcsrev(str));
   return 0;
}If _MBCS has been defined, GENTEXT.C maps to the following MBCS program:/*
* MBCSGTXT.C: use of generic-text mappings defined in TCHAR.H
*            Generic-Text-Mapping example program
*            MBCS version of GENTEXT.C
*/#include <stdlib.h>
#include <direct.h>int __cdecl main(int argc, char **argv, char **envp)
{
   char buff[_MAX_PATH];
   char *str = "Astring";
   char *amsg = "Reversed";
   wchar_t *wmsg = L"Is";   printf("MBCS version\n");   if (_getcwd(buff, _MAX_PATH) == NULL) {
       printf("Can't Get Current Directory - errno=%d\n", errno);
   }
   else {
       printf("Current Directory is '%s'\n", buff);
   }   printf("'%s' %hs %ls:\n", str, amsg, wmsg);
   printf("'%s'\n", _mbsrev(str));
   return 0;
}If _UNICODE has been defined, GENTEXT.C maps to the following Unicode version of the program. For more information about using wmain in Unicode programs as a replacement for main, see Using wmain in C Language Reference./*
* UNICGTXT.C: use of generic-text mappings defined in TCHAR.H
*            Generic-Text-Mapping example program
*            Unicode version of GENTEXT.C
*/#include <stdlib.h>
#include <direct.h>int __cdecl wmain(int argc, wchar_t **argv, wchar_t **envp)
{
   wchar_t buff[_MAX_PATH];
   wchar_t *str = L"Astring";
   char *amsg = "Reversed";
   wchar_t *wmsg = L"Is";   printf("Unicode version\n");   if (_wgetcwd(buff, _MAX_PATH) == NULL) {
      printf("Can't Get Current Directory - errno=%d\n", errno);
   }
   else {
       wprintf(L"Current Directory is '%s'\n", buff);
   }   wprintf(L"'%s' %hs %ls:\n", str, amsg, wmsg);
   wprintf(L"'%s'\n", wcsrev(str));
   return 0;
}If neither _MBCS nor _UNICODE has been defined, GENTEXT.C maps to single-byte ASCII code, as follows:/*
* SBCSGTXT.C: use of generic-text mappings defined in TCHAR.H
*            Generic-Text-Mapping example program
*            Single-byte (SBCS) Ascii version of GENTEXT.C
*/#include <stdlib.h>
#include <direct.h>int __cdecl main(int argc, char **argv, char **envp)
{
   char buff[_MAX_PATH];
   char *str = "Astring";
   char *amsg = "Reversed";
   wchar_t *wmsg = L"Is";   printf("SBCS version\n");   if (_getcwd(buff, _MAX_PATH) == NULL) {
       printf("Can't Get Current Directory - errno=%d\n", errno);
   }
   else {
       printf("Current Directory is '%s'\n", buff);
   }   printf("'%s' %hs %ls:\n", str, amsg, wmsg);
   printf("'%s'\n", strrev(str));
   return 0;
}See Also   Generic-text mappings, Data type mappings, Constants and global variable mappings, Routine mappings, Using generic-text mappingsEND Microsoft Specific

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"_T"有什么用?怎么使用？

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