This example uses the WinSetModalWindow to set a system modal window.

#define INCL_WINWINDOWMGR
#include <OS2.H>
HWND hwndSysModal;

/*  Input processing can enter a "system modal" state. In */
/*  this state, all pointing  device and keyboard input   */
/*  is directed to a special window, known as the         */
/*  system-modal window. Typically, this will be a dialog */
/*  window requiring input.                               */

WinSetSysModalWindow(HWND_DESKTOP,hwndSysModal);