php案例：json新增数据

<?php

   $json_string= '[{"id":"1","name":"cyg","age":"27","subject":"海南学校"},{"id":"2","name":"liwen","age":"21","subject":"北京学校"}]';
$data = json_decode($json_string,true);// 把JSON字符串转成PHP数组
//新增一个数据到某个json的某个下标中
$data['0']["mmmm"]="aas";//在json里面的下标0中，新增一个数据mmmm
$json_strings = json_encode($data);
var_dump($json_strings);