Main Window Creation

Every Win32-based application must have a WinMain function as its entry point. WinMain performs a number of tasks, including registering the window class for the main window and creating the main window. WinMain registers the main window class by calling the RegisterClass function, and it creates the main window by calling the CreateWindowEx function.

Portability Issue The entry point need not be named WinMain.

Your WinMain function can also limit your application to a single instance. Create a named mutex using CreateMutex. If GetLastError returns ERROR_ALREADY_EXISTS, another instance of your application exists (it created the mutex) and you should exit your WinMain.

Windows does not automatically display the main window after creating it; instead, an application must use the ShowWindow function to display the main window. After creating the main window, the application's WinMain function calls ShowWindow, passing it two parameters: the handle of the main window and a flag specifying whether the main window should be minimized or maximized when it is first displayed. Normally, the flag can be set to any of the constants beginning with the SW_ prefix. However, when ShowWindow is called to display the application's main window, the flag must be set to SW_SHOWDEFAULT. This flag tells Windows to display the window as directed by the program that started the application.

If a window is created as a Unicode window, it receives only Unicode messages. To determine if a window is a Unicode window, call IsWindowUnicode.

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