Create a json object for every cycle

[giorgioloi]

Hello! I'm trying to create a new json object for every loop in the while, (every while loop is a processed frame with a different data). I want to create a Json like this:
frame.json

[
"0":{
    "age": 28.1982421875,
    "male prob": 0.9951171875,
    "id": 0 }
},
"1":{
    "age": 31.1982421875,
    "male prob": 0.8851171888,
    "id": 0 }
]

or
frame.json

[{
    "age": 28.1982421875,
    "male prob": 0.9951171875,
    "id": 0 },
{
    "age": 31.1982421875,
    "male prob": 0.8851171888,
    "id": 0 }
]

main.cpp

#include "json.hpp"
#include <iostream>
#include <fstream>
using json = nlohmann::json;

int main(){
json j;
int framecnt = 0;
while (true)
    {
        //...frame-processing
        
        j.push_back(json::object_t::value_type("id", idx));
        j.push_back(json::object_t::value_type("male prob", r.maleProb));
        j.push_back(json::object_t::value_type("age", r.age));

        std::ofstream o("frame.json");
        o << std::setw(4) << j << std::endl;
       framecnt++;
    }
}

With the push_back I have always one object, what can I use for an output like that?
Sorry I'm not very familiar with c++ and this library. Thanks!

[dota17]

for the second:

[{
    "age": 28.1982421875,
    "male prob": 0.9951171875,
    "id": 0 },
{
    "age": 31.1982421875,
    "male prob": 0.8851171888,
    "id": 0 }
]

the code should be

#include "json.hpp"
#include <iostream>
#include <fstream>
using json = nlohmann::json;

int main(){
json j;
int framecnt = 0;
while (true)
    {
        //...frame-processing
        json tmp;
       tmp["id"] = idx;
       tmp["male prob"] = r.maleProb;
       tmp["age"] = r.age;

        j.push_back(tmp);

        std::ofstream o("frame.json");
        o << std::setw(4) << j << std::endl;
       framecnt++;
    }
}

[giorgioloi]

Thank you so much! It works :)