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Using wmain

Microsoft Specific

In the Unicode programming model, you can define a wide-character version of the main function. Use wmain instead of main if you want to write portable code that adheres to the Unicode programming model.

Like main, several restrictions apply to the wmain function that don't apply to any other C functions. The wmain function:

  • Can't be declared as inline.
  • Can't be declared as static.
  • Can't have its address taken.
  • Can't be called from your program.

The wmain function signature

The wmain function doesn't have a declaration, because it's built into the language. If it did, the declaration syntax for wmain would look like this:

int wmain( void );
int wmain( int argc, wchar_t *argv[ ] );
int wmain( int argc, wchar_t *argv[ ], wchar_t *envp[ ] );

The wmain function is declared implicitly by using one of these signatures. You may use any of these signatures when you define your wmain function. You can then pass wide-character arguments and, optionally, a wide-character environment pointer to the program. The Microsoft compiler also allows wmain to have a return type of void when no value is returned. The argv and envp parameters to wmain can also be defined as type wchar_t**. For more information about the arguments, see Argument description.

The envp environment

If your program uses a main function, the multibyte-character environment is created by the run-time library 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, a wide-character environment is created at program startup and is pointed to by the _wenviron global variable. An MBCS (ASCII) environment is created on the first call to _putenv or getenv, and is pointed to by the _environ global variable.

For more information on the MBCS environment, see Internationalization.

END Microsoft Specific

See also

main function and program execution