$get_token_url = 'https://api.weixin.qq.com/sns/oauth2/access_token?appid='.$appid.'&secret='.$secret.'&code='.$code.'&grant_type=authorization_code';

$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);

curl_close($ch);

$json_obj = json_decode($res,true);

//根据openid和access_token查询用户信息

 $ac = $json_obj['access_token'];

$openid = $json_obj['openid'];

echo $openId ;