Is it safe to return string.c_str() received from get()?

[apivovarov]

What do you want to achieve?

I'm building a function const char* GetName(id).

Data is stored in json file, e.g. [{"name":"N1"}, {"name":"N2"}, {"name":"N3"}]

Is it safe for my function to return c_str pointers from std::string received from get()? I'm not sure about std::string objects lifecycle inside nlohmann::json.

Example:

nlohmann::json metadata;  // will be alive till the end of the program
jsonFile >> metadata;

const char* GetName(int id) {
  return metadata[id]["name"].get<std::string>().c_str();
}

[nlohmann]

With the current code, you make a copy of the stored string and hence return a temporary.

Do this instead:

const char* GetName(int id) {
  return metadata[id]["name"].get_ref<std::string&>().c_str();
}

[apivovarov]

Looks like get_ref type should be const std::string&. My GetName method is actually const method const char* GetName(int id) const

const char* GetName(int id) const {
  return metadata[id]["name"].get_ref<const std::string&>().c_str();
}

[nlohmann]

Ok, does this fix the issue for you?

[apivovarov]

Yes, Thank you for your help!