-extern uschar *string_append(uschar *, int *, int *, int, ...);
-extern uschar *string_append_listele(uschar *, uschar, const uschar *);
-extern uschar *string_append_listele_n(uschar *, uschar, const uschar *, unsigned);
+extern uschar *string_append(uschar *, int *, int *, int, ...) WARN_UNUSED_RESULT;
+extern uschar *string_append_listele(uschar *, int *, int *, uschar, const uschar *) WARN_UNUSED_RESULT;
+extern uschar *string_append_listele_n(uschar *, int *, int *, uschar, const uschar *, unsigned) WARN_UNUSED_RESULT;