This example uses WinEnableWindow to enable the system menu window for the given parent window, after verifying that the parent window handle is valid (WinIsWindow), belongs to the calling thread (WinIsThreadActive), and is not presently enabled (WinIsWindowEnabled).

#define INCL_WINWINDOWMGR       /* Window Manager Functions     */
#define INCL_WINFRAMEMGR        /* Window Frame Functions       */
#include <os2.h>

HAB   hab;              /* anchor-block handle                  */
HWND    hwndSysmenu;    /* system menu window                   */
HWND    hwnd;           /* parent window                        */
BOOL  fSuccess;         /* success indicator                    */

/* if handle specifies a valid window and the window belongs to the
   current thread, query the enabled status of the system menu */
if (WinIsWindow(hab, hwnd) && WinIsThreadActive(hab))
   {
   /* obtain handle for system menu */
   hwndSysmenu = WinWindowFromID(hwnd,FID_SYSMENU);

   /* if system menu is not enabled, enable it */
   if (!WinIsWindowEnabled(hwndSysmenu))
      fSuccess = WinEnableWindow(hwndSysmenu, TRUE);
   }