<?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 );  
            //偏移指针到索引位置读取4个字节  
            fseek( $fd, $useripbegin + 7 * $Middle );  
            $useripData1 = fread( $fd, 4 );  
            if ( strlen( $useripData1 ) < 4 ) {  
                fclose( $fd );  
                return 'File Error';  
            }  
            //提取出来的数据转换成长整形，如果数据是负数则加上2的32次幂  
            $userip1num = implode( '', unpack( 'L', $useripData1 ) );  
            if ( $userip1num < 0 )  
                $userip1num += pow( 2, 32 );  
            //提取的长整型数大于我们IP地址则修改结束位置进行下一次循环  
            if ( $userip1num > $useripNum ) {  
                $EndNum = $Middle;  
                continue;  
            }  
            //取完上一个索引后取下一个索引  
            $DataSeek = fread( $fd, 3 );  
            if ( strlen( $DataSeek ) < 3 ) {  
                fclose( $fd );  
                return 'File Error';  
            }  
            $DataSeek = implode( '', unpack( 'L', $DataSeek . chr( 0 ) ) );  
            fseek( $fd, $DataSeek );  
            $useripData2 = fread( $fd, 4 );  
            if ( strlen( $useripData2 ) < 4 ) {  
                fclose( $fd );  
                return 'File Error';  
            }  
            $userip2num = implode( '', unpack( 'L', $useripData2 ) );  
            if ( $userip2num < 0 )  
                $userip2num += pow( 2, 32 );  
            //找不到IP地址对应城市  
            if ( $userip2num < $useripNum ) {  
                if ( $Middle == $BeginNum ) {  
                    fclose( $fd );  
                    return 'No Data';  
                }  
                $BeginNum = $Middle;  
            }  
        }  
        $useripFlag = fread( $fd, 1 );  
        if ( $useripFlag == chr( 1 ) ) {  
            $useripSeek = fread( $fd, 3 );  
            if ( strlen( $useripSeek ) < 3 ) {  
                fclose( $fd );  
                return 'System Error';  
            }  
            $useripSeek = implode( '', unpack( 'L'