php post json数据

function http_post_data($url, $data_string) {  
    $ch = curl_init();  
    curl_setopt($ch, CURLOPT_POST, 1);  
    curl_setopt($ch, CURLOPT_URL, $url);  
    curl_setopt($ch, CURLOPT_POSTFIELDS, $data_string);  
    curl_setopt($ch, CURLOPT_HTTPHEADER, array(  
      'Content-Type: application/json; charset=utf-8',  
      'Content-Length: ' . strlen($data_string))  
    );  
    ob_start();  
    curl_exec($ch);  
    $return_content = ob_get_contents();  
    ob_end_clean();  
    $return_code = curl_getinfo($ch, CURLINFO_HTTP_CODE);  
    return array($return_code, $return_content);  
}  
    $url  = "http://www.xxxx.com";  
    $data = json_encode(array('cmd'=>"Query_Ranking_Sys",'group'=>1,'room'=>0,'name'=>"RoomSvr",'value'=>array(0=>array('key'=>5,'beginindex'=>0,'count'=>10))));   
    list($return_code, $return_content) = http_post_data($url, $data);