PHP获取访问ip自定义函数

function getip(){
     if (getenv ( "HTTP_CLIENT_IP" ) && strcasecmp ( getenv ( "HTTP_CLIENT_IP" ), "unknown" ))
        $ip = getenv ( "HTTP_CLIENT_IP" );
    else if (getenv ( "HTTP_X_FORWARDED_FOR" ) && strcasecmp ( getenv ( "HTTP_X_FORWARDED_FOR" ), "unknown" ))
        $ip = getenv ( "HTTP_X_FORWARDED_FOR" );
    else if (getenv ( "REMOTE_ADDR" ) && strcasecmp ( getenv ( "REMOTE_ADDR" ), "unknown" ))
        $ip = getenv ( "REMOTE_ADDR" );
    else if (isset ( $_SERVER ['REMOTE_ADDR'] ) && $_SERVER ['REMOTE_ADDR'] && strcasecmp ( $_SERVER ['REMOTE_ADDR'], "unknown" ))
         $ip = $_SERVER ['REMOTE_ADDR'];
    else
        $ip = "unknown";
    return ($ip);
}