This function posts a message to a message queue.

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

HMQ       hmq;  /*  Message-queue handle. */
ULONG     msg;  /*  Message identifier. */
MPARAM    mp1;  /*  Parameter 1. */
MPARAM    mp2;  /*  Parameter 2. */
BOOL      rc;   /*  Success indicator. */

rc = WinPostQueueMsg(hmq, msg, mp1, mp2);