HWND SetActiveWindow( );
See SetActiveWindow in the Win32 SDK.
Remarks
Activates the window.
Example
// The following example attaches a HWND to the CWindow object
// and sets the window as an active window by calling
// CWindow::SetActiveWindow which returns the HWND of the
// previously active window.
CWindow myWindow;
myWindow.Attach(hWndFoo);
HWND hWndPrev = myWindow.SetActiveWindow();