NAME

       rpmatch - determine if the answer to a question is affirmative or negative

LIBRARY

       Standard C library (libc, -lc)

SYNOPSIS

       #include <stdlib.h>

       int rpmatch(const char *response);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       rpmatch():
           Since glibc 2.19:
               _DEFAULT_SOURCE
           glibc 2.19 and earlier:
               _SVID_SOURCE

DESCRIPTION

       rpmatch()   handles   a   user   response  to  yes  or  no  questions,  with  support  for
       internationalization.

       response should be a null-terminated string containing a user-supplied  response,  perhaps
       obtained with fgets(3) or getline(3).

       The  user's  language preference is taken into account per the environment variables LANG,
       LC_MESSAGES, and LC_ALL, if the program has called setlocale(3) to effect their changes.

       Regardless of the locale, responses matching ^[Yy] are always accepted as affirmative, and
       those matching ^[Nn] are always accepted as negative.

RETURN VALUE

       After examining response, rpmatch() returns 0 for a recognized negative response ("no"), 1
       for a recognized positive  response  ("yes"),  and  -1  when  the  value  of  response  is
       unrecognized.

ERRORS

       A  return  value  of  -1 may indicate either an invalid input, or some other error.  It is
       incorrect to only test if the return value is nonzero.

       rpmatch() can fail for any of the reasons that regcomp(3)  or  regexec(3)  can  fail;  the
       cause  of  the error is not available from errno or anywhere else, but indicates a failure
       of the regex engine (but this case is indistinguishable from that of an unrecognized value
       of response).

ATTRIBUTES

       For an explanation of the terms used in this section, see attributes(7).

       ┌────────────────────────────────────────────────────────┬───────────────┬────────────────┐
       │Interface                                               │ Attribute     │ Value          │
       ├────────────────────────────────────────────────────────┼───────────────┼────────────────┤
       │rpmatch()                                               │ Thread safety │ MT-Safe locale │
       └────────────────────────────────────────────────────────┴───────────────┴────────────────┘

STANDARDS

       rpmatch() is not required by any standard, but available under the GNU C library, FreeBSD,
       and AIX.

BUGS

       The YESEXPR and NOEXPR of some locales (including "C") only inspect the first character of
       the  response.   This  can  mean  that  "yno" et al. resolve to 1.  This is an unfortunate
       historical side-effect which should be fixed in time with proper localisation, and  should
       not deter from rpmatch() being the proper way to distinguish between binary answers.

EXAMPLES

       The  following  program displays the results when rpmatch() is applied to the string given
       in the program's command-line argument.

       #define _DEFAULT_SOURCE
       #include <locale.h>
       #include <stdio.h>
       #include <stdlib.h>
       #include <string.h>

       int
       main(int argc, char *argv[])
       {
           if (argc != 2 || strcmp(argv[1], "--help") == 0) {
               fprintf(stderr, "%s response\n", argv[0]);
               exit(EXIT_FAILURE);
           }

           setlocale(LC_ALL, "");
           printf("rpmatch() returns: %d\n", rpmatch(argv[1]));
           exit(EXIT_SUCCESS);
       }

SEE ALSO

       fgets(3), getline(3), nl_langinfo(3), regcomp(3), setlocale(3)