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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(): _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).

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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