test_nlohmann_json.cpp

#include <fstream>
#include <iostream>
#include <libnotify.h>
#include <nlohmann/json.hpp>

#ifdef __clang__
static constexpr auto COMPILER = "clang++";
#else
static constexpr auto COMPILER = "g++";
#endif

using namespace std;

struct coordinate_t {
  double x;
  double y;
  double z;

  auto operator<=>(const coordinate_t &) const = default;

  friend ostream &operator<<(ostream &out, const coordinate_t &point) {
    out << "coordinate_t {x: " << point.x << ", y: " << point.y
        << ", z: " << point.z << "}";
    return out;
  }
};

string read_file(const string &filename) {
  ifstream file{filename};
  if (!file.good()) {
    return {};
  }
  return string{istreambuf_iterator<char>{file}, {}};
}

coordinate_t calc(const string &text) {
  auto x = 0.0, y = 0.0, z = 0.0;
  auto len = 0;

  auto jv = nlohmann::json::parse(text);
  auto &obj = jv["coordinates"];
  for (auto &coord : obj) {
    len += 1;
    x += coord["x"].get<double>();
    y += coord["y"].get<double>();
    z += coord["z"].get<double>();
  }

  return coordinate_t{x / len, y / len, z / len};
}

int main() {
  auto right = coordinate_t{2.0, 0.5, 0.25};
  for (auto v : {R"({"coordinates":[{"x":2.0,"y":0.5,"z":0.25}]})",
                 R"({"coordinates":[{"y":0.5,"x":2.0,"z":0.25}]})"}) {
    auto left = calc(v);
    if (left != right) {
      cerr << left << " != " << right << endl;
      exit(EXIT_FAILURE);
    }
  }

  const auto &text = read_file("/tmp/1.json");

  const auto &results = notifying_invoke([&]() { return calc(text); },
                                         "C++/{} (Nlohmann)", COMPILER);

  cout << results << endl;
}