This function waits for a filtered message.

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

HAB      hab;      /*  Anchor-block handle. */
ULONG    ulFirst;  /*  First message identity. */
ULONG    ulLast;   /*  Last message identity. */
BOOL     rc;       /*  Success indicator. */

rc = WinWaitMsg(hab, ulFirst, ulLast);