Manpages - rpmatch.3

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

  #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

*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.

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.

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).

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

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

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)$.

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);
  }

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

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