POSIX正则表达式 验证电子邮件地址

/*
 * regex.c - 用正则表达式验证电子邮件地址
 *
 *          POSIX正则表达式
 *
 *
 * 编译命令：
 *         gcc regex.c -o regex -Wall
 *
 *
 *              Copyright  叶剑飞 2012
 *
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <regex.h>     /* regular expression 正则表达式 */

#define MAX_LENGTH 1000

int main (void)
{
    size_t char_num;
    char email_address[MAX_LENGTH];
    char user_name[MAX_LENGTH];
    char domain_name[MAX_LENGTH];

    regmatch_t pmatch[4];
    regex_t match_regex;

    regcomp( &match_regex,"([0-9A-Za-z-_.]+)@([0-9a-z]+.[a-z]{2,3}(.[a-z]{2})?)",REG_EXTENDED );

    while ( scanf( "%s",email_address ) != EOF )
    {
        if ( regexec( &match_regex,email_address,4,pmatch,0 ) == 0 )
        {
            char_num = pmatch[1].rm_eo - pmatch[1].rm_so;
            strncpy( user_name,&(email_address[pmatch[1].rm_so]),char_num );
            user_name[char_num] = '';

            char_num = pmatch[2].rm_eo - pmatch[2].rm_so;
            strncpy( domain_name,&(email_address[pmatch[2].rm_so]),char_num );
            domain_name[char_num] = '';

            puts( "您输入的电子邮件地址合法" );
            printf ( "用户名：%sn",user_name );
            printf ( "域名：%snn",domain_name );
        }
        else
            puts( "您输入的电子邮件地址不合法nn" );
    }

    regfree( &match_regex );
    return EXIT_SUCCESS;
}