Regular expressions in C: examples?

Question

I\'m after some simple examples and best practices of how to use regular expressions in ANSI C. man regex.h does not provide that much help.

Answer 1

This is an example of using REG_EXTENDED. This regular expression

"^(-)?([0-9]+)((,|.)([0-9]+))?\n$"

Allows you to catch decimal numbers in Spanish system and international. :)

#include 
#include 
#include 
regex_t regex;
int reti;
char msgbuf[100];

int main(int argc, char const *argv[])
{
    while(1){
        fgets( msgbuf, 100, stdin );
        reti = regcomp(®ex, "^(-)?([0-9]+)((,|.)([0-9]+))?\n$", REG_EXTENDED);
        if (reti) {
            fprintf(stderr, "Could not compile regex\n");
            exit(1);
        }

        /* Execute regular expression */
        printf("%s\n", msgbuf);
        reti = regexec(®ex, msgbuf, 0, NULL, 0);
        if (!reti) {
            puts("Match");
        }
        else if (reti == REG_NOMATCH) {
            puts("No match");
        }
        else {
            regerror(reti, ®ex, msgbuf, sizeof(msgbuf));
            fprintf(stderr, "Regex match failed: %s\n", msgbuf);
            exit(1);
        }

        /* Free memory allocated to the pattern buffer by regcomp() */
        regfree(®ex);
    }

}