This function is used to process messages while a dialog is active.

#include <os2.h>

#define INCL_WIN
#define INCL_WINDIALOGS
#define IDD_OPEN WM_USER+200
#define IDM_OPEN WM_USER+201

HWND hwndDlg;
HWND hwndFrame;
PFNWP OpenDlg;

/* Inside client procedure */
switch(msg)
{
  case WM_COMMAND:
       /* The user has chosen a menu item.   */
       /* Process the selection accordingly. */
       switch (SHORT1FROMMP(mp1))
       {
         case IDM_OPEN:
              if (WinDlgBox(HWND_DESKTOP,
                            hwndFrame,    /* Handle of the owner         */
                            OpenDlg,      /* Dialog procedure address    */
                            (ULONG)0,     /* Location of dialog resource */
                            IDD_OPEN,     /* Resource identifier         */
                            NULL))        /* Application-specific data   */
         {
           WinProcessDlg(hwndDlg);
         }
         break;
       }
       break;
}