NAME

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

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 │
       └──────────┴───────────────┴────────────────┘

CONFORMING TO

       rpmatch() is not required by any standard, but is available on a few other systems.

BUGS

       The rpmatch() implementation looks at only the first character of response.   As  a  consequence,  "nyes"
       returns  0,  and  "ynever;  not  in  a  million years" returns 1.  It would be preferable to accept input
       strings much more strictly, for example (using the extended  regular  expression  notation  described  in
       regex(7)): ^([yY]|yes|YES)$ and ^([nN]|no|NO)$.

EXAMPLE

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

       #define _SVID_SOURCE
       #include <locale.h>
       #include <stdlib.h>
       #include <string.h>
       #include <stdio.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)

COLOPHON

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