This function invokes the default dialog procedure with hwndDlg, msg, mp1, and mp2.

#define INCL_WINDIALOGS /* Or use INCL_WIN, INCL_PM, Also in COMMON section */
#include <os2.h>

HWND       hwndDlg;    /*  Dialog-window handle. */
ULONG      msg;        /*  Message identity. */
MPARAM     mp1;        /*  Parameter 1. */
MPARAM     mp2;        /*  Parameter 2. */
MRESULT    mresReply;  /*  Message-return data. */

mresReply = WinDefDlgProc(hwndDlg, msg, mp1,
              mp2);