PHP Ajax跨域问题解决办法

XMLHttpRequest cannot load http://server.runoob.com/server.php. No 'Access-Control-Allow-Origin' header is present on the requested 
resource.Origin 'http://client.runoob.com' is therefore not allowed access.

//允许单个域名访问
header("Access-Control-Allow-Origin:http://www.yourdomain.com");

//或者下面这种，允许多个域名访问
$origin = isset($_SERVER['HTTP_ORIGIN']) ? $_SERVER['HTTP_ORIGIN'] : '';
$allow_origin = array(
    'http://www.yourdomain1.com',  
    'http://www.yourdomain2.com'
);
if(in_array($origin, $allow_origin))
{  
    header('Access-Control-Allow-Origin:'.$origin);       
}

//或者下面这种，允许所有可访问
header("Access-Control-Allow-Origin:*");

Header set Access-Control-Allow-Origin *
#意思是对这个域名的资源进行访问时，添加一个头信息