Short: Happy undocumented quirks

Description of AdjustWindowRectEx() on MSDN:

The AdjustWindowRect function calculates the required size of the window rectangle, based on the desired client-rectangle size. The window rectangle can then be passed to the CreateWindow function to create a window whose client area is the desired size.

Description of GetWindowRect() on MSDN:

The GetClientRect function retrieves the coordinates of a window’s client area. The client coordinates specify the upper-left and lower-right corners of the client area. Because client coordinates are relative to the upper-left corner of a window’s client area, the coordinates of the upper-left corner are (0,0).

You would think that these functions are eachothers counterpart, you give a clientrectangle to AdjustWindowRectEx(), say (200×200) and you’ll get something like 214×234 if you have the Vista look active on your window. When you set your window to those dimensions with for example SetWindowPos(), and afterwards you check the size with GetClientRect(), you’ll get 212×232. This works the same with other themes, and if you copy-paste a screenshot into MS Paint, you’ll be able to measure the same 212×232 while the outside of the window is the exact given 214×234 – properly set by SetWindowPos().

The dirty ugly solution of course is to add 2 pixels to whatever you get back from AdjustWindowRectEx() – but surely someone at Microsoft is supposed to Test these functions?

RECT size;
size.left	= myWindowObj->x;
size.top	= myWindowObj->y;
size.right	= size.left + myWindowObj->w;
size.bottom	= size.top + myWindowObj->h;

AdjustWindowRectEx( &size, GetWindowLong(hWND, GWL_STYLE), FALSE, GetWindowLong(hWND, GWL_EXSTYLE) );
SetWindowPos( hWND, NULL, myWindowObj->x, myWindowObj->y, size.right - size.left + 2, size.bottom - size.top + 2, SWP_NOZORDER | SWP_NOACTIVATE );