In Win32, How can I detect if a HWND is a dialog?

Question

In a pure C Win32 application, how can I detect if a HWND is a dialog?

Answer 1

Use GetClassLong() to find its class atom. Unless it was created with a custom window class (very unlikely), its class will be WC_DIALOG.

if ( WC_DIALOG == MAKEINTATOM(GetClassLong(hWnd, GCW_ATOM)) )
{
    /* this is a dialog */
}

Answer 2

Dialogs have a standard class name of "#32770". You can use GetClassName()/RealGetWindowClass() ¹ to check if a window is using a dialog class.

^{1: see What makes RealGetWindowClass so much more real than GetClassName?}