除了可以通过at，还可以通过[ ]运算符来读取和设置object/array

#include <iostream>
#include <nlohmann/json.hpp>
using namespace std;
using json = nlohmann::json;
 
int main()
{
    json data = R"({
        "name": "xiaoming",
        "age": 10, 
        "parent":   
        [
            {
                "father" : "zhang",
                "age" : 40
            },
            {
                "mother" : "wang",
                "age" : 36
            }
        ]
    })"_json;
 
    cout<<data["name"]<<endl;
    cout<<data["parent"][0]["age"]<<endl;
    data["parent"][0]["age"] = 42;
    cout<<data<<endl;
    return 0;
}

运行程序输出：

"xiaoming"
40
{"age":10,"name":"xiaoming","parent":