The $UPDREC function is used in conjunction with the ON FIELD CONSTRAINT CONFLICT unit. Use $UPDREC in conjunction with $UNQREC to find the record number of the unique record already stored ($UNQREC) and the record number of the non-unique record you are attempting to store ($UPDREC).
If $UPDREC is invoked from an ON FCC unit following the detection of a field-level constraint conflict, it returns the file-relative number of the record whose update causes the conflict. In all other cases, $UPDREC returns a -1. The $UPDREC function takes no arguments.