PHP 获取客户端IP

function get_ip()
{
    static $realIP;
    if (isset($_SERVER)){
        if (isset($_SERVER["HTTP_X_FORWARDED_FOR"])){
            $realIP = explode(',', $_SERVER["HTTP_X_FORWARDED_FOR"]);
            $realIP = $realIP[0];
        } else if (isset($_SERVER["HTTP_CLIENT_IP"])) {
            $realIP = $_SERVER["HTTP_CLIENT_IP"];
        } else {
            $realIP = $_SERVER["REMOTE_ADDR"];
        }
    } else {
        if (getenv("HTTP_X_FORWARDED_FOR")){
            $realIP = getenv("HTTP_X_FORWARDED_FOR");
        } else if (getenv("HTTP_CLIENT_IP")) {
            $realIP = getenv("HTTP_CLIENT_IP");
        } else {
            $realIP = getenv("REMOTE_ADDR");
        }
    }
    $_SERVER['REMOTE_ADDR'] = $realIP;
    return $realIP;
}