Json: Conversion error for std::map<int, std::string>

[MariaRamos89]

Hi,

I'm trying to save a std::map into a json, and then the json is saved in a file.

nlohmann::json db;
db = mymap;
std::ofstream output_file(filename);
output_file << std::setw(4) << db << std::endl;

The problem is the result of the json:

I'm expecting this kind of output:
{ 1 : "one", 2 : "two"}
However, the result is:
[ [1, "one"], [2, "two"]]

So, when in other program I'm trying to read that file and try to save it in a json for doing the conversion to std::map again, I'm having the next error:

error: ambiguous overload for ‘operator=’ (operand types are ‘std::map<int, std::__cxx11::basic_string<char> >’ and ‘nlohmann::json {aka nlohmann::basic_json<>}’)

I've been looking in similar errors like #607, but I don't find a solution.
I've tried to build the map manually but the output is the same. Maybe I'm missing something.

Thanks in advance

[nlohmann]

Keys of JSON objects must be strings:

The library does not convert the keys of the std::map to strings automatically, and under the hood a list of pairs is the closest we can get inside JSON. You need to make the conversion yourself, e.g. with code like

for (auto it = mymap.begin(); it != mymap.end(); ++it)
{
  db[std::to_string(it->first)] = it->second;
}

[MariaRamos89]

Thanks,
Now it's working :)

[lucaszanella]

I'm actually ok with [ [1, "one"], [2, "two"]] but I cant make it work: https://github.com/nlohmann/json/discussions/2378. Any ideas on why?

[nlohmann]

Nothing broken here:

    std::map<int, std::string> m;
    m[1] = "one";
    m[2] = "two";
    std::cout << json(m) << std::endl;

Output:

[[1,"one"],[2,"two"]]