如何解决php curl 没有返回值的问题?

php使用curl访问https返回无结果的问题

最近在做一个微信自动登录，发起验证以后回调页面获取openid时 curl函数返回空。

$appid = "appid appid "; 
$secret = "secret "; 
$code = $_GET["code"]; 
$get_token_url = 'https://api.weixin.qq.com/sns/oauth2/access_token?appid='.$appid.'&secret='.$secret.'&code='.$code.'&grant_type=authorization_code';
//header("location:$get_token_url");
echo $get_token_url."<BR>";
$ch = curl_init();
curl_setopt($ch,CURLOPT_URL,$get_token_url); 
curl_setopt($ch,CURLOPT_HEADER,0); 
curl_setopt($ch,CURLOPT_RETURNTRANSFER,1 ); 
curl_setopt($ch,CURLOPT_CONNECTTIMEOUT,10); 
$res = curl_exec($ch); 
echo "echo:".json_encode($res)."<br>";     //显示false
echo curl_multi_getcontent($ch)."<br>";   //空
curl_close($ch);                     
$json_obj = json_decode($res,true); 
//根据openid和access_token查询用户信息 
$access_token = $json_obj['access_token']; 
$openid = $json_obj['openid']; 
var_dump($res);                                                     //显示obj(false)
echo $openid;

结果curl无返回值，最终百度到一片文章 http://yanda.net.cn/articles/453 文章中提到

改成如下问题解决

$ch = curl_init();
curl_setopt($ch,CURLOPT_URL,$get_token_url);
curl_setopt($ch,CURLOPT_HEADER,0); 
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false); //不验证证书
curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, false); //不验证证书
curl_setopt($ch,CURLOPT_RETURNTRANSFER,1 ); 
curl_setopt($ch,CURLOPT_CONNECTTIMEOUT,10); 
$res = curl_exec($ch); 
var_dump($res);  //有返回值