-int ri_append(struct rline *li, char *format, ...);
-int ri_error(struct rline *li, int error_code, char *format, ...);
+int ri_append(struct rline *li, char *format, ...) __attribute__ ((format (printf, 2, 3)));
+int ri_error(struct rline *li, int error_code, char *format, ...) __attribute__ ((format (printf, 3, 4)));