This example uses WinIsControlEnabled to determine if a selected control is valid; if it is not, an error message box is displayed.

#define INCL_WINWINDOWMGR   /* Window Manager Functions                  */
#define INCL_WINDIALOGS     /* Window Dialog Mgr Functions               */
#include <os2.h>

HWND    hwndDlg;            /* Dialog window                             */
MPARAM  mp1;                /* Parameter 1                               */
USHORT  usId;               /* Dialog control id                         */

case WM_CONTROL:
     usId = SHORT1FROMMP(mp1);
     if (!WinIsControlEnabled(hwndDlg, usId))
        {
          WinMessageBox(HWND_DESKTOP,
                        hwndDlg,                 /* Client-window handle */
                        "Control is not valid",  /* Body of the message  */
                        "Error notification",    /* Title of the message */
                        0,                       /* Message box id       */
                        MB_NOICON |              /* Button flag          */
                        MB_OK);                  /* Icon flag            */
        }