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;}