TCHAR.H

this header file isn't part of the ANSI C standard, hence every function and macro definition defined is preceded by an underscore. this header provides a set of alternative names for the normal run-time library functions requiring string parameters

EXAMPLE CONTENTS

//if _UNICODE is defined
#define _tcslen wcslen
typedef wchar_t TCHAR;
#define __T(x) L##x

//if _UNICODE is not defined
#define _tcslen strlen
typedef char TCHAR;
#define __T(x) x

 * the pair of number signed (##) is called a "token paste". it causes the letter L
   to be appended to the macro parameter
    - if the macro parameter is "Hello!", then L##x is L"Hello!"