This function posts a message to the message queue associated with the window defined by hwnd.

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

HWND      hwnd;      /*  Window handle. */
ULONG     ulMsgid;   /*  Message identity. */
MPARAM    mpParam1;  /*  Parameter 1. */
MPARAM    mpParam2;  /*  Parameter 2. */
BOOL      rc;        /*  Message-posted indicator. */

rc = WinPostMsg(hwnd, ulMsgid, mpParam1, mpParam2);