CreateWindow

CreateWindow is a Win32 API function in the User32 library that creates a window and returns a handle to it (HWND). It requires a previously registered window class and is commonly used to instantiate top-level and child windows in a Windows desktop application.

The function signature takes parameters that specify the window class, window title, style flags, position, size, parent window, menu handle, application instance, and an optional pointer that is passed to the window procedure. CreateWindow is equivalent to calling CreateWindowEx with dwExStyle set to 0.

On success, the function returns a valid HWND. If it fails, it returns NULL and the error code can be retrieved with GetLastError. The created window is not shown by default; developers typically call ShowWindow and UpdateWindow after creation.

A window procedure associated with the registered class handles messages for the window. The lpParam value is accessible to the WM_CREATE message via CREATESTRUCT, and can be used to pass initialization data to the window.

Notes: Use CreateWindowEx when you need extended styles or to be explicit about Unicode or ANSI variants. Ensure the window class is registered, and use the proper instance handle (hInstance). For Unicode builds, prefer CreateWindowW with a wide-class name.

Example:

HWND hwnd = CreateWindow("MyClass", "My Window", WS_OVERLAPPEDWINDOW, CW_USEDEFAULT, CW_USEDEFAULT, 800, 600, NULL, NULL, hInstance, NULL);

ShowWindow(hwnd, SW_SHOW);

UpdateWindow(hwnd);