You declare formal parameters to wmain using a similar format to main. You can then pass wide-character arguments and, optionally, a wide-character environment pointer to the program. The argv and envp parameters to wmain are of type wchar_t*.
If your program uses a main function, the multibyte-character environment is created by the operating system at program startup. A wide-character copy of the environment is created only when needed (for example, by a call to the _wgetenv or _wputenv functions). On the first call to _wputenv, or on the first call to _wgetenv if an MBCS environment already exists, a corresponding wide-character string environment is created and is then pointed to by the _wenviron global variable, which is a wide-character version of the _environ global variable. At this point, two copies of the environment (MBCS and Unicode) exist simultaneously and are maintained by the operating system throughout the life of the program.
Similarly, if your program uses a wmain function, an MBCS (ASCII) environment is created on the first call to _putenv or getenv, and is pointed to by the _environ global variable.
You can also use _tmain, which is defined in TCHAR.h. _tmain will resolve to main unless _UNICODE is defined, in which case _tmain will resolve to wmain.
