C语言实现电子邮件地址验证程序

/*
 * 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] = '\0';

  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] = '\0';

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

 regfree( &match_regex );
 return EXIT_SUCCESS;
}