Casting of json value results in std::domain_error

Question

I am trying to iterate over an array in a json file to retrieve an entry with an ID. The value that I want to compare it to is not a string (the json default type), but an uint64_t. For testing purposes, I wrote this simplified example:

#include <iostream>
#include <nlohmann/json.hpp>

using json = nlohmann::json;

int main ()
{
    std::string file = "test.json";
    std::ifstream ifs(file);
    json j = json::parse(ifs);

    std::string s = "10";
    int i = 10;

    for (auto it : j["inputs"]) {
        std::cout << "value: " << it["id"] << std::endl;

        if (it["id"] == s) {
            std::cout << "matching" << std::endl;
        }

        if (it["id"].get<int>() == i) {
            std::cout << "also matching numeric" << std::endl;
        }
    }
}

As you can see, I tried using ints first, because that is probably a more commonly used type. However, I am unable to cast the value I get from the ID-field to any other type. I get the following output:

value: "10"
matching
terminate called after throwing an instance of 'std::domain_error'
  what():  type must be number, but is string
Abgebrochen (Speicherabzug geschrieben)

I would like to know what I have to do to correctly cast entries of the json to an arbitrary data type. Thanks!

The test json:

{
   "inputs": [
      {
         "type": "camera",
         "id": "10"
      },
      {
         "type": "lidar",
         "stream_id": "20"
      }
   ],
   "outputs": [
   ]
}

Answer 1

What version are you using? Because I got next output on latest version:

value: 10
also matching numeric
value: null
terminate called after throwing an instance of 'nlohmann::detail::type_error'
  what():  [json.exception.type_error.302] type must be number, but is null
Aborted (core dumped)