正则表达式实现（Linux C语言版本）

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <regex.h>

/* The following is the size of a buffer to contain any error messages
encountered when the regular expression is compiled. */

#define MAX_ERROR_MSG 0x1000

/* Compile the regular expression described by "regex_text" into
"r". */

static int compile_regex (regex_t * r, const char * regex_text)
{
int status = regcomp (r, regex_text, REG_EXTENDED|REG_NEWLINE);
if (status != 0) {
char error_message[MAX_ERROR_MSG];
regerror (status, r, error_message, MAX_ERROR_MSG);
printf ("Regex error compiling '%s': %s\n",
regex_text, error_message);
return 1;
}
return 0;
}

/*
Match the string in "to_match" against the compiled regular
expression in "r".
*/

static int match_regex (regex_t * r, const char * to_match)
{
/* "P" is a pointer into the string which points to the end of the
previous match. */
const char * p = to_match;
/* "N_matches" is the maximum number of matches allowed. */
const int n_matches = 10;
/* "M" contains the matches found. */
regmatch_t m[n_matches];

while (1) {
int i = 0;
int nomatch = regexec (r, p, n_matches, m, 0);
if (nomatch) {
printf ("No more matches.\n");
return nomatch;
}
for (i = 0; i < n_matches; i++) {
int start;
int finish;
if (m[i].rm_so == -1) {
break;
}
start = m[i].rm_so + (p - to_match);
finish = m[i].rm_eo + (p - to_match);
if (i == 0) {
printf ("$& is ");
}
else {
printf ("$%d is ", i);
}
printf ("'%.*s' (bytes %d:%d)\n", (finish - start),
to_match + start, start, finish);
}
p += m[0].rm_eo;
}
return 0;
}

int main(int argc, char ** argv)
{
regex_t r;
const char * regex_text;
const char * find_text;
if (argc != 3) {
regex_text = "([[:digit:]]+)[^[:digit:]]+([[:digit:]]+)";
find_text = "This 1 is nice 2 so 33 for 4254";
}
else {
regex_text = argv[1];
find_text = argv[2];
}
printf ("Trying to find '%s' in '%s'\n", regex_text, find_text);
compile_regex(& r, regex_text);
match_regex(& r, find_text);
regfree (& r);
return 0;
}