php判断用户客户端是否是微信内置客户端

在iPhone下，返回

Mozilla/5.0 (iPhone; CPU iPhone OS 5_1 like Mac OS X) AppleWebKit/534.46 (KHTML, like Gecko) Mobile/9B176 MicroMessenger/4.3.2

在Android下，返回

Mozilla/5.0 (Linux; U; Android 2.3.6; zh-cn; GT-S5660 Build/GINGERBREAD) AppleWebKit/533.1 (KHTML, like Gecko) Version/4.0 Mobile Safari/533.1 MicroMessenger/4.5.255

	function is_weixin()

{ 
    if ( strpos($_SERVER['HTTP_USER_AGENT'], 'MicroMessenger') !== false ) {
        return true;
    }  
        return false;
}