Windows and Messages.

This is my version of this.

I just make it shorter than msdn’s version and contains only what are important for me.


In a graphical Windows-based application, a window is a rectangular area of the screen where the application displays output and receives input from the user. Therefore, one of the first tasks of a graphical Windows-based application is to create a window.

A window shares the screen with other windows, including those from other applications. Only one window at a time can receive input from the user. The user can use the mouse, keyboard, or other input device to interact with this window and the application that owns it.


When creating any window, the system sends messages to the window procedure for the window. The system sends the WM_NCCREATE message after creating the window’s nonclient area and the WM_CREATE message after creating the client area. The window procedure receives both messages before the system displays the window. Both messages include a pointer to a CREATESTRUCT structure that contains all the information specified in the CreateWindowEx function. Typically, the window procedure performs initialization tasks upon receiving these messages.

When creating a child window, the system sends the WM_PARENTNOTIFY message to the parent window after sending the WM_NCCREATE and WM_CREATE messages. It also sends other messages while creating a window. The number and order of these messages depend on the window class and style and on the function used to create the window. These messages are described in other topics in this help file.


A Windows-based application can have multiple threads of execution, and each thread can create windows. The thread that creates a window must contain the code for its window procedure.

An application can use the EnumThreadWindows function to enumerate the windows created by a particular thread. This function passes the handle to each thread window, in turn, to an application-defined callback function, EnumThreadWndProc.

The GetWindowThreadProcessId function returns the identifier of the thread that created a particular window.

To set the show state of a window created by another thread, use the ShowWindowAsync function.


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