WinMain info  Overview  Group

The WinMain function is called by the system as the initial entry point for a Win32-based application.

int WINAPI WinMain(

HINSTANCE hInstance,	// handle to current instance
HINSTANCE hPrevInstance,	// handle to previous instance
LPSTR lpCmdLine,	// pointer to command line
int nCmdShow	// show state of window
);

Parameters

hInstance

Identifies the current instance of the application.

hPrevInstance

Identifies the previous instance of the application. For a Win32-based application, this parameter is always NULL. If you need to detect whether another instance already exists, create a uniquely named mutex using the CreateMutex function. CreateMutex will succeed even if the mutex already exists, but the GetLastError function will return ERROR_ALREADY_EXISTS. This indicates that another instance of your application exists, because it created the mutex first.

lpCmdLine

Points to a null-terminated string specifying the command line for the application, excluding the program name. To retrieve the entire command line, use the GetCommandLine function.

nCmdShow

Specifies how the window is to be shown. This parameter can be one of the following values:

Value	Meaning
SW_HIDE	Hides the window and activates another window.
SW_MINIMIZE	Minimizes the specified window and activates the top-level window in the system’s list.
SW_RESTORE	Activates and displays a window. If the window is minimized or maximized, Windows restores it to its original size and position (same as SW_SHOWNORMAL).
SW_SHOW	Activates a window and displays it in its current size and position.
SW_SHOWMAXIMIZED	Activates a window and displays it as a maximized window.
SW_SHOWMINIMIZED	Activates a window and displays it as an icon.
SW_SHOWMINNOACTIVE	Displays a window as an icon. The active window remains active.
SW_SHOWNA	Displays a window in its current state. The active window remains active.
SW_SHOWNOACTIVATE	Displays a window in its most recent size and position. The active window remains active.
SW_SHOWNORMAL	Activates and displays a window. If the window is minimized or maximized, Windows restores it to its original size and position (same as SW_RESTORE).

Return Values

If the function succeeds, terminating when it receives a WM_QUIT message, it should return the exit value contained in that message’s wParam parameter. If the function terminates before entering the message loop, it should return zero.

Remarks

Your WinMain should initialize the application, display its main window, and enter a message retrieval-and-dispatch loop that is the top-level control structure for the remainder of the application’s execution. Terminate the message loop when it receives a WM_QUIT message. At that point, your WinMain should exit the application, returning the value passed in the WM_QUIT message’s wParam parameter. If WM_QUIT was received as a result of calling PostQuitMessage, the value of wParam is the value of the PostQuitMessage function’s nExitCode parameter. For more information, see Creating a Message Loop.

ANSI applications can use the lpCmdLine parameter of the WinMain function to access the command-line string, excluding the program name. The reason that WinMain cannot return Unicode strings is that lpCmdLine uses the LPSTR data type, not the LPTSTR data type. The GetCommandLine function can be used to access Unicode strings in the command line, because it uses the LPTSTR data type.

See Also

CreateMutex, DispatchMessage, GetCommandLine, GetMessage, PostQuitMessage, TranslateMessage