The OS/2 version of AdjustWindowRectEx does not emulate the Windows 32-bit version. Instead, the OS/2 function calculates the amount of adjustment necessary to accommodate the window that CreateWindow places on the screen, so long as the caller passes the same rectangle structure pointer and style parameters to AdjustWindowRectEx and CreateWindow.
Note: In Windows, if you call AdjustWindowRectEx with a NULL style parameter (to indicate the Overlapped style), Windows does not adjust the rectangle. Yet, if CreateWindow is called with the same NULL style parameter, a caption is added. If the caller tries to use the rectangle returned by AdjustWindowRectEx to size a window of this style, the sizing is off when the window is created. Many other style parameters are treated with this kind of inconsistency in Windows. In terms of window sizing, Windows is consistent with itself only where dialogs and overlapped windows are concerned. These are the only kinds of windows that really have client areas in Windows.