Given handle of a Win32 window, I need to find position of it relative to its parent window.

I know several functions (e.g.; GetWindowRect() and GetClientRect()), but none of them explicitly return the desired coordinates.

How do I do this?

The solution is using the combined power of GetWindowRect() and MapWindowPoints().

GetWindowRect() retrieves the coordinates of a window relative to the entire screen area you see on your monitor. We need to convert these absolute coordinates into relative coordinates of our main window area. The MapWindowPoints() transforms the coordinates given relative to one window into relative to another. So we need a "handle" of the screen area and the handle of the parent window of the control which we are trying to find coordinates of. The screen are is a "window" in Windows terminology and it is called "Desktop". We can access the handle of Desktop by the constant HWND_DESKTOP defined in WinUser.h (including Windows.h is enough). And we can get the handle of our parent window simply by calling the Win32 function GetParent(). Now we have all the parameters required to call the MapWindowPoints() function.

MapWindowPoints() is defined as:

MapWindowPoints() transform the coordinates relatively from hWndFrom to hWndTo. In our case, we do the transformation from Desktop (HWND_DESKTOP) to our parent window (GetParent(hWnd)). Therefore, the resulting RECT structure holds the relative coordinates of our child window (hWnd) relative to its parent window.

that is the solution I am using either for windows or for controls (child windows)

I know it's been answered before, but it's much easier to just get a child window's rect in screen coordinates, get it's position (POINT ptCWPos = {rectCW.left, rectCW.top};) and use the ScreenToClient() function, that will transform the screen coordinate point to the window's client coordinate point:

PS: I know that looks like a lot more code, but most of it is fiddling with the rect position; in most cases one will actually need the rect position rather than the whole rect.