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GetClientRect - Retrieve Window Size in Windows
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The way to retrieve the window size in Windows API is through the GetClientRect.
This functions retrieves the coordinates of a window's client area. That means an area that we actually can draw into, without border, menus and anything else outside users (client) interaction.
See some example:
RECT rect; GetClientRect(window, &rect); int width = rect.right - rect.left; int height = rect.bottom - rect.top;