Different JSON printouts for empty dictionary on Linux and Mac.

[canaknesil]

• What is the issue you have?

When I create JSON string with this statement json j = {{}}; and print it, [null]is printed on Linux, while [{}] is printed on Mac. I think the Linux one is erroneous.

• Please describe the steps to reproduce the issue. Can you provide a small but working code example?

main.cpp:

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

using json = nlohmann::json;
using namespace std;

int main()
{
  json j = {{}};
  cout << j << endl;

  return 0;
}

Compiled with g++ -std=c++11 main.cpp.

• What is the expected behavior?

The expected behavior is that both printouts should be [{}].

• And what is the actual behavior instead?

I get [null] when I run the same code on Linux.

• Which compiler and operating system are you using? Is it a supported compiler?

Linux operating system: Ubuntu 18.04.4 LTS
Linux compiler: g++ (Ubuntu 7.5.0-3ubuntu1~18.04) 7.5.0

Mac operating system: macOS Catalina Version 10.15.3
Mac compiler: Apple clang version 11.0.0 (clang-1100.0.33.17)

• Did you use a released version of the library or the version from the develop branch?

I am using release version 3.7.3.

• If you experience a compilation error: can you compile and run the unit tests?

No error while compilation.

[nlohmann]

This is a known issue that the compilers (GCC and Clang) interpret the braces differently. There is little I can do about this. If you want the JSON [{}], then the safest would be json::array(json()) or "[{}]"_json. Sorry about the inconvenience.

[t-b]

@nlohmann Do you have a link for that known issue?

[nlohmann]

Latest is #2046 which also works on a solution.