Example of POSIX regex in C

I just wanted to show an example of using regular expressions in C.

#include <sys/types.h>
#include <regex.h>

int regcomp(regex_t *preg, const char *regex, int cflags);
	Prepare your regex for fast processing
int regexec(const regex_t *preg, const char *string, size_t nmatch, regmatch_t pmatch[], int eflags);
	Do the matching
void regfree(regex_t *preg);
	Free your compiled regex for a new "compiling"
size_t regerror(int errcode, const regex_t *preg, char *errbuf, size_t errbuf_size);
	Retrieve some more information on why the regexec() failed

#include <sys/types.h>
#include <regex.h>
#include <stdio.h>

int main(int argc, char *argv[]){
        regex_t regex;
        int reti;
        char msgbuf[100];

/* Compile regular expression */
        reti = regcomp(&regex, "^a[[:alnum:]]", 0);
        if( reti ){ fprintf(stderr, "Could not compile regex\n"); exit(1); }

/* Execute regular expression */
        reti = regexec(&regex, "abc", 0, NULL, 0);
        if( !reti ){
        else if( reti == REG_NOMATCH ){
                puts("No match");
                regerror(reti, &regex, msgbuf, sizeof(msgbuf));
                fprintf(stderr, "Regex match failed: %s\n", msgbuf);

/* Free compiled regular expression if you want to use the regex_t again */

        return 0;

Author Per-Olof Pettersson

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