Changing the default format for unordered_map (or other set)

[Enduriel]

What do you want to achieve?

I'm looking to use the library to save the state of a game simulation I'm working on. My knowledge of C++ is fairly basic (have only just begun shifting over from C# and Java) and I have been unable to find anyone else looking to achieve the same thing so I'm turning to here.

I'm trying to keep the save files easily and quickly readable with reasonable success. My only issue is with the way maps are converted, and I was wondering if there was a way to change the format without having to manually define a different from and to _json for every type.

When saving the unordered_map instead of having it a map as

[
        [
            "food",
            5.0
        ],
        [
            "amenities",
            10.0
        ]
]

is there an easy way to format this to

        ["food": 5.0],
        ["amenities": 10.0],

for all key value combinations? I have been unable to find anything about this anywhere so finally decided to reach out here as I've seen people be very helpful regarding questions.

• Compiler: VS 2019 C++17
• Operating system: Windows 10
• latest release version 3.7.3

[nlohmann]

What is the exact type of which the serialization is

[
        [
            "food",
            5.0
        ],
        [
            "amenities",
            10.0
        ]
]

?

[Enduriel]

void to_json(json& j, const Resource& resource) {
    j = resource.content;
}
//within Resource
std::unordered_map<ResourceType, double> content;

and ResourceType is an enum where I have set up enum to string (rather than int) serialization, to clarify though, this was still the formatting when the enum was represented as an int.

EDIT: I'm pretty tired and my brain is clearly not functioning properly: To state it simply, that is a serialization of the unordered_map content shown above.

[nlohmann]

I see. Since the keys are not convertible to std::string, the map is translated into a list of pairs. You could try two things:

• Define an implicit conversion of ResourceType to std::string. This could (haven't tested) yield to a conversion to a JSON object.
• Define a translation for std::unordered_map<ResourceType, double> via an adl_serializer, see https:/nlohmann/json#how-do-i-convert-third-party-types.

[Enduriel]

The problem with option 2 is that from what I understand I would have to do that for every new way I stored objects together so 1 sounds a lot more viable, but I can't find any way to set up implicit enum to std::string conversion anywhere online.

[nlohmann]

Sorry, I forgot that it's not possible to provide a operator std::string() to an enum. So you may be left with option 2.

[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.