This function sets the message interest of a window class.

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

HAB      hab;           /*  Anchor-block handle. */
PSZ      pszClassName;  /*  Window-class name. */
ULONG    ulMsgClass;    /*  Message class to have interest level set. */
LONG     lControl;      /*  Interest identifier for the message class. */
BOOL     rc;            /*  Interest-changed indicator. */

rc = WinSetClassMsgInterest(hab, pszClassName,
       ulMsgClass, lControl);