+
+/* Same as argmatch, but upon failure, report an explanation of the
+ failure, and exit using the function EXIT_FN. */
+
+ptrdiff_t __xargmatch_internal (char const *context,
+ char const *arg, char const *const *arglist,
+ char const *vallist, size_t valsize,
+ argmatch_exit_fn exit_fn);
+
+/* Programmer friendly interface to __xargmatch_internal. */
+
+# define XARGMATCH(Context, Arg, Arglist, Vallist) \
+ ((Vallist) [__xargmatch_internal (Context, Arg, Arglist, \
+ (char const *) (Vallist), \
+ sizeof *(Vallist), \
+ argmatch_die)])
+