怎么使用post提交json数据

$post_data =   <br />
            array(  <br />
                    'name'=>'aaa',  <br />
                    'age'=>45,  <br />
            );  <br />
  <br />
<br />
    $url='http://www.example.com/example.php';  <br />
  <br />
    $ch = curl_init();  <br />
    curl_setopt($ch, CURLOPT_POST, 1);  <br />
    curl_setopt($ch, CURLOPT_URL,$url);  <br />
    curl_setopt($ch, CURLOPT_POSTFIELDS, $post_data);  <br />
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);<br />
    $result=curl_exec($ch);  <br />
    echo $result;