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JSON_DISABLE_ENUM_SERIALIZATION

#define JSON_DISABLE_ENUM_SERIALIZATION /* value */

When defined to 1, default serialization and deserialization functions for enums are excluded and have to be provided by the user, for example, using NLOHMANN_JSON_SERIALIZE_ENUM (see arbitrary type conversions for more details).

Parsing or serializing an enum will result in a compiler error.

This works for both unscoped and scoped enums.

Default definition

The default value is 0.

#define JSON_DISABLE_ENUM_SERIALIZATION 0

Notes

CMake option

Enum serialization can also be controlled with the CMake option JSON_DisableEnumSerialization (OFF by default) which defines JSON_DISABLE_ENUM_SERIALIZATION accordingly.

Examples

Example 1: Disabled behavior

The code below forces the library not to create default serialization/deserialization functions from_json and to_json, meaning the code below does not compile.

#define JSON_DISABLE_ENUM_SERIALIZATION 1
#include <nlohmann/json.hpp>

using json = nlohmann::json;

enum class Choice
{
    first,
    second,
};

int main()
{
    // normally invokes to_json serialization function but with JSON_DISABLE_ENUM_SERIALIZATION defined, it does not
    const json j = Choice::first; 

    // normally invokes from_json parse function but with JSON_DISABLE_ENUM_SERIALIZATION defined, it does not
    Choice ch = j.get<Choice>();
}
Example 2: Serialize enum macro

The code below forces the library not to create default serialization/deserialization functions from_json and to_json, but uses NLOHMANN_JSON_SERIALIZE_ENUM to parse and serialize the enum.

#define JSON_DISABLE_ENUM_SERIALIZATION 1
#include <nlohmann/json.hpp>

using json = nlohmann::json;

enum class Choice
{
    first,
    second,
};

NLOHMANN_JSON_SERIALIZE_ENUM(Choice,
{
    { Choice::first, "first" },
    { Choice::second, "second" },
})

int main()
{
    // uses user-defined to_json function defined by macro
    const json j = Choice::first; 

    // uses user-defined from_json function defined by macro
    Choice ch = j.get<Choice>();
}
Example 3: User-defined serialization/deserialization functions

The code below forces the library not to create default serialization/deserialization functions from_json and to_json, but uses user-defined functions to parse and serialize the enum.

#define JSON_DISABLE_ENUM_SERIALIZATION 1
#include <nlohmann/json.hpp>

using json = nlohmann::json;

enum class Choice
{
    first,
    second,
};

void from_json(const json& j, Choice& ch)
{
    auto value = j.get<std::string>();
    if (value == "first")
    {
        ch = Choice::first;
    }
    else if (value == "second")
    {
        ch = Choice::second;
    }
}

void to_json(json& j, const Choice& ch)
{
    auto value = j.get<std::string>();
    if (value == "first")
    {
        ch = Choice::first;
    }
    else if (value == "second")
    {
        ch = Choice::second;
    }
}

int main()
{
    // uses user-defined to_json function
    const json j = Choice::first; 

    // uses user-defined from_json function
    Choice ch = j.get<Choice>();
}

See also

Version history

  • Added in version 3.11.0.

Last update: September 18, 2022