Documentation on operator[] behavior with missing keys

[sachabest]

• What is the issue you have?

Right now operator[key] is documented to create a null key in the called upon json object should key not exist in that object, if the source object is NOT const. If the object is const, operator[] returns the equivalent of *(map.cend()).

I think the documentation around this could be improved, as I would bet users are not fully aware of the behavioral differences depending on the constness of the source object.

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

#include <nlohmann/json.hpp>

int main()
{
    const nlohmann::json j = {{ "key1", "value1" }}; // { "key1": "value1" }
    const nlohmann::json& missingKey = j["key2"];
    // missingKey here is UB
}

• What is the expected behavior?

I think the current behavior is fine, documentation could be improved to reflect it.

• And what is the actual behavior instead?

N/A

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

GCC 5 + RHEL7 as well as VC141/151 Win10 x64

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

Latest major version

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

[nlohmann]

The function (https://github.com/nlohmann/json/blob/develop/include/nlohmann/json.hpp#L3280) has a @warning documentation:

    @warning If the element with key @a key does not exist, the behavior is
    undefined.

Any proposal how to improve this?

[sonulohani]

Documentation seems right. While accessing any key through operator [], we need to make sure that given key is in range, otherwise it will result in undefined behaviour and can also crash application.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.