PHP根据IP地址获取所在城市具体实现

文件目录：

ipLocation
-----qqwry
----------QQWry.Dat
-----ipCity.class.php

ipCity.class.php文件代码：
代码如下:
<?php

class ipCity {

    /**
     * 根据ip地址获取对应所在城市
     * @param type $userip 用户IP地址
     * @return string
     */
    public function getCity( $userip, $dat_path = '' ) {
        //IP数据库路径，这里用的是QQ IP数据库 20110405 纯真版
        empty( $dat_path ) && $dat_path = FCPATH . 'plugin/ipLocation/qqwry/QQWry.Dat';
        //判断IP地址是否有效
        if ( preg_match( "/^([0-9]{1,3}.){3}[0-9]{1,3}$/", $userip ) == 0 ) {
            return 'IP Address Invalid';
        }
        //打开IP数据库
        if ( !$fd = @fopen( $dat_path, 'rb' ) ) {
            return 'IP data file not exists or access denied';
        }
        //explode函数分解IP地址，运算得出整数形结果
        $userip = explode( '.', $userip );
        $useripNum = $userip[0] * 16777216 + $userip[1] * 65536 + $userip[2] * 256 + $userip[3];
        //获取IP地址索引开始和结束位置
        $DataBegin = fread( $fd, 4 );
        $DataEnd = fread( $fd, 4 );
        $useripbegin = implode( '', unpack( 'L', $DataBegin ) );
        if ( $useripbegin < 0 )
            $useripbegin += pow( 2, 32 );
        $useripend = implode( '', unpack( 'L', $DataEnd ) );
        if ( $useripend < 0 )
            $useripend += pow( 2, 32 );
        $useripAllNum = ($useripend - $useripbegin) / 7 + 1;
        $BeginNum = 0;
        $EndNum = $useripAllNum;
        //使用二分查找法从索引记录中搜索匹配的IP地址记录
        while ( $userip1num > $useripNum || $userip2num < $useripNum ) {
            $Middle = intval( ($EndNum + $BeginNum) / 2 );