wchar_t

wchar_t是Unicode字符的数据类型，2个字节。

typedef unsigned short wchar_t;

另外,

typedef char    CHAR;
typedef wchar_t WCHAR; 

为了让编译器识别Unicode字符串，必须以在前面加一个“L”,例如:

wchar_t *szTest=L"This is a Unicode string."

_UNICODE

The following project setting in General page describes which Character Set is to be used for compilation: (General -> Character Set)

Use Unicode Character Set

This way, when your project is being compiled as Unicode, the TCHAR would translate to wchar_t.
If it is being compiled as ANSI/MBCS, it would be translated to char.
You are free to use char and wchar_t, and project settings will not affect any direct use of these keywords.

如果VS中选择Use Unicode Character Set，TCHAR按照wchar_t执行；如果选择是Use Multi-Byte Charactor Set，TCHAR按照char执行。

#ifdef _UNICODE
typedef wchar_t TCHAR;
#else
typedef char TCHAR;
#endif

TCHAR函数

    TCHAR tchBuffer[1024] = {0};
    _tcsncpy_s(tchBuffer, 1024, L"Hello", 3);
    printf("_tcsncpy_s(tchBuffer, 1024, L\"Hello\", 3) : %S\n", tchBuffer);

    _stprintf_s(tchBuffer, 1024, L"Beijing %d", 2008);
    printf("_stprintf_s : %S\n", tchBuffer);

    _tcscpy_s(tchBuffer, 1024, L"Hello");
    _tcscat_s(tchBuffer, 1024, L" World");
    _tcsncat_s(tchBuffer, 1024, L"1234", 3);
    printf("tchBuffer:%S\n", tchBuffer);
    printf("sizeof(tchBuffer) : %d\n", sizeof(tchBuffer));
    printf("_tcslen(tchBuffer) : %d\n", _tcslen(tchBuffer));

    TCHAR tchBuffer2[1024] = L"Hello World";
    int nRet = _tcscmp(tchBuffer, tchBuffer2);
    if (0 == nRet)
    {
        printf("_tcscmp(%S, %S) == 0\n", tchBuffer, tchBuffer2);
    }
    else
    {
        printf("_tcscmp(%S, %S) != 0\n", tchBuffer, tchBuffer2);
    }

    nRet = _tcsncmp(tchBuffer, tchBuffer2, 5);
    if (0 == nRet)
    {
        printf("_tcsncmp(%S, %S, 5) == 0\n", tchBuffer, tchBuffer2);
    }
    else
    {
        printf("_tcsncmp(%S, %S, 5) != 0\n", tchBuffer, tchBuffer2);
    }

    nRet = _tcsicmp(L"HELLO", L"Hello");
    if (0 == nRet)
    {
        printf("_tcsicmp(L\"HELLO\", L\"Hello\") == 0\n");
    }
    else
    {
        printf("_tcsicmp(L\"HELLO\", L\"Hello\") != 0\n");
    }

    nRet = _tcsnicmp(L"HELLO", L"Hello", 3);
    if (0 == nRet)
    {
        printf("_tcsnicmp(L\"HELLO\", L\"Hello\", 3) == 0\n");
    }
    else
    {
        printf("_tcsnicmp(L\"HELLO\", L\"Hello\", 3) != 0\n");
    }

    TCHAR str[64] = _T("1234d56d789");
    LPTSTR substr = _tcschr(str, _T('d')); 
    printf(" _tcschr(%S, _T('d') : %S\n", str, substr);

    LPTSTR substr2 = _tcsrchr(str, _T('d'));
    printf("_tcsrchr(%S, _T('d') : %S\n", str, substr2);

运行结果

References:

http://blog.csdn.net/wangqifeng10_16/article/details/5784811
http://blog.csdn.net/wskelan/article/details/5017131
https://www.codeproject.com/Articles/76252/What-are-TCHAR-WCHAR-LPSTR-LPWSTR-LPCTSTR-etc