converting std::chrono::system_clock::time_point to json.

[victor-psiori]

What do you want to achieve?

I was trying to convert time variable of my custom class which is std::chrono::system_clock::time_point type, to a json.

I am able to convert other class variable which are strings. The class outline looks like this:
SensorData(std::chrono::system_clock::time_point t, const std::string& topic, const std::string& frame_id)
After going through the README, I believe converting third party type is the relevant section for me. I have scratched the surface a bit, but yet to go deeper.
I have two questions:
i. Could you confirm whether this is the right section to look for regarding the mentioned use case.
ii. Are there examples available here which does a similar task?

Please let me know if something is not clear here.
Thanks.

What have you tried?

I have tried creating object as mentioned in README following a key-value pair pattern.

Can you provide a small code example?

`json j;
j["topic"] = topic;
j["frame_id"] = frame_id;
j["t"] = t; //here i get error: " no viable overloaded '=' "`

Which compiler and operating system are you using?

• Compiler: Apple LLVM version 10.0.1 (clang-1001.0.46.4)
• Operating system: mac os
  Target: x86_64-apple-darwin18.7.0
  Thread model: posix

Which version of the library did you use?

• [ x] latest release version 3.7.3
• other release - please state the version: ___
• the develop branch

[nlohmann]

This is the section you need: https://github.com/nlohmann/json#how-do-i-convert-third-party-types

Example:

#include <iostream>
#include <chrono>
#include "json.hpp"

using json = nlohmann::json;

namespace nlohmann {
    template<typename Clock, typename Duration>
    struct adl_serializer<std::chrono::time_point<Clock, Duration>>
    {
        static void to_json(json& j, const std::chrono::time_point<Clock, Duration>& tp)
        {
            j["since_epoch"] = std::chrono::duration_cast<std::chrono::microseconds>(tp.time_since_epoch()).count();
            j["unit"] = "microseconds";
        }
    };
}

int main()
{
    auto time_point_now = std::chrono::high_resolution_clock::now();
    json j = time_point_now;
    std::cout << j << std::endl;
}

Output:

{"since_epoch":1732154346,"unit":"microseconds"}

[victor-psiori]

oh yes, this works. Thanks a lot for the response.

[paulocoutinhox]

Hi,

Do you have the from_json method?