Inserting in unordered json using a pointer retains the leading slash

[emanuel-raad]

What is the issue you have?

Inserting a node in an unordered json object using a pointer retains the leading slash

Please describe the steps to reproduce the issue.

I am using the single json.hpp file

Can you provide a small but working code example?

using json = nlohmann::json;
using ojson = nlohmann::ordered_json;
using json_pointer = nlohmann::json::json_pointer;

std::string p = "/root";

json test1;
test1[json_pointer(p)] = json::object();
std::cout << test1 << '\n';

ojson test2;
test2[json_pointer(p)] = json::object();
std::cout << test2 << '\n';

I also tested with "/root"_json_pointer instead of json_pointer(p) and I get the same behaviour.

What is the expected behavior?

Output from the code above:

{"root":{}}
{"/root":{}}

And what is the actual behavior instead?

I expect both outputs to be the same, without the leading forward slash:

{"root":{}}
{"root":{}}

Which compiler and operating system are you using?

• Compiler: MSVC\14.28.29910
• Operating system: Windows 10\19043.1165

Which version of the library did you use?

• latest release version 3.10.0
• other release - please state the version: ___
• the develop branch

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

Not a compilation error.

• yes
• no - please copy/paste the error message below

[nlohmann]

The reason for this behavior is that you use a nlohmann::json::json_pointer with a nlohmann::unordered_json:

ojson test2;
test2[json_pointer(p)] = json::object();

There are two overloads for ordered_json::operator[]: one for strings and one for nlohmann:: unordered_json::json_pointer. As json_pointer(p) is not of the latter type, but has an implicit conversion to std::string, the former overload is used with /root.

You can fix this by changing the type of the JSON Pointer in the second example:

ojson test2;
test2[ojson::json_pointer(p)] = json::object();

[emanuel-raad]

Thanks for the explanation about the overloads! I switched to using nlohmann:: unordered_json::json_pointer and it works now