This function broadcasts a message to multiple windows.

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

HWND      hwndParent;  /*  Parent-window handle. */
ULONG     ulMsgId;     /*  Message identifier. */
MPARAM    mpParam1;    /*  Parameter 1. */
MPARAM    mpParam2;    /*  Parameter 2. */
ULONG     flCmd;       /*  Broadcast message command. */
BOOL      rc;          /*  Success indicator. */

rc = WinBroadcastMsg(hwndParent, ulMsgId,
       mpParam1, mpParam2, flCmd);