PHP实例——获取客户端IP地址

function get_client_ip() {
    static $ip = NULL;
    if ($ip !== NULL) return $ip;
    if (isset($_SERVER['HTTP_X_FORWARDED_FOR'])) {
        $arr = explode(',', $_SERVER['HTTP_X_FORWARDED_FOR']);
        $pos =  array_search('unknown',$arr);
        if(false !== $pos) unset($arr[$pos]);
        $ip   =  trim($arr[0]);
    }elseif (isset($_SERVER['HTTP_CLIENT_IP'])) {
        $ip = $_SERVER['HTTP_CLIENT_IP'];
    }elseif (isset($_SERVER['REMOTE_ADDR'])) {
        $ip = $_SERVER['REMOTE_ADDR'];
    }
    // IP地址合法验证
    $ip = (false !== ip2long($ip)) ? $ip : '0.0.0.0';
    return $ip;
}