The SetActiveWindow function activates a window. The window must be associated with the calling thread's message queue.
HWND SetActiveWindow(
HWND hWnd // handle to window to activate
);
If the function succeeds, the return value is the handle to the window that was previously active.
If the function fails, the return value is NULL. To get extended error information, call GetLastError.
The SetActiveWindow function activates a window, but not if the application is in the background. The window will be brought into the foreground (top of Z order) if the application is in the foreground when it sets the activation.
If the window identified by the hWnd parameter was created by the calling thread, the active window status of the calling thread is set to hWnd. Otherwise, the active window status of the calling thread is set to NULL.
The SetForegroundWindow window function, on the other hand, activates a window and forces it into the foreground. An application should only call SetForegroundWindow if it needs to display critical errors or information that needs the user's immediate attention .
By using the AttachThreadInput function, a thread can attach its input processing to another thread. This allows a thread to call SetActiveWindow to activate a window associated with another thread's message queue.
Windows NT: Requires version 3.1 or later.
Windows: Requires Windows 95 or later.
Windows CE: Requires version 1.0 or later.
Header: Declared in winuser.h.
Import Library: Use user32.lib.
Keyboard Input Overview, Keyboard Input Functions, GetActiveWindow, SetForegroundWindow, WM_ACTIVATE