PHP 二维array转换json

PHP提供函数直接将array转换成json

json_encode($param_array);

若需要下面这种嵌套式如何处理呢？

{
    "appid": "1500001105",
    "nonce": 32490,
    "timestamp": 1458195253,
    "signature": "bf13fe77f46a96edba1a0e2b84fce66580b2f50b",
    "param": {
        "userid": "bonnie"
    }
}

先构成一个二级array，再调用json_encode转换即可。

$param = array(
    "userid"=>"bonnie"
);
$params = array(
    "appid"=>"1500001105",
    "nonce"=>$nonce,
    "timestamp"=>$timestamp,
    "signature"=>$signature,
    "param"=>$param,
);
$params_json = json_encode($params);