+/**
+ * opt_log_stderr_exit - print message to stderr, then exit(1)
+ * @fmt: printf-style format.
+ *
+ * Just like opt_log_stderr, only then does exit(1). This means that
+ * when handed to opt_parse, opt_parse will never return false.
+ *
+ * Example:
+ * // This never returns false; just exits if there's an erorr.
+ * opt_parse(&argc, argv, opt_log_stderr_exit);
+ */
+void opt_log_stderr_exit(const char *fmt, ...);
+