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2.6 KiB
2.6 KiB
NLOHMANN_JSON_SERIALIZE_ENUM
#define NLOHMANN_JSON_SERIALIZE_ENUM(type, conversion...)
By default, enum values are serialized to JSON as integers. In some cases this could result in undesired behavior. If an enum is modified or re-ordered after data has been serialized to JSON, the later de-serialized JSON data may be undefined or a different enum value than was originally intended.
The NLOHMANN_JSON_SERIALIZE_ENUM allows to define a user-defined serialization for every enumerator.
Parameters
type(in)- name of the enum to serialize/deserialize
conversion(in)- a pair of an enumerator and a JSON serialization; arbitrary pairs can can be given as comma-separated list
Default definition
The macros add two friend functions to the class which take care of the serialization and deserialization:
template<typename BasicJsonType>
inline void to_json(BasicJsonType& j, const type& e);
template<typename BasicJsonType>
inline void from_json(const BasicJsonType& j, type& e);
Notes
!!! info "Prerequisites"
The macro must be used inside the namespace of the enum.
!!! important "Important notes"
- When using [`get<ENUM_TYPE>()`](../basic_json/get.md), undefined JSON values will default to the first specified
conversion. Select this default pair carefully. See example 1 below.
- If an enum or JSON value is specified in multiple conversions, the first matching conversion from the top of the
list will be returned when converting to or from JSON. See example 2 below.
Examples
??? example "Example 1: Basic usage"
The example shows how `NLOHMANN_JSON_SERIALIZE_ENUM` can be used to serialize/deserialize both classical enums and
C++11 enum classes:
```cpp hl_lines="16 17 18 19 20 21 22 29 30 31 32 33"
--8<-- "examples/nlohmann_json_serialize_enum.cpp"
```
Output:
```json
--8<-- "examples/nlohmann_json_serialize_enum.output"
```
??? example "Example 2: Multiple conversions for one enumerator"
The example shows how to use multiple conversions for a single enumerator. In the example, `Color::red` will always
be *serialized* to `"red"`, because the first occurring conversion. The second conversion, however, offers an
alternative *deserialization* from `"rot"` to `Color::red`.
```cpp hl_lines="17"
--8<-- "examples/nlohmann_json_serialize_enum_2.cpp"
```
Output:
```json
--8<-- "examples/nlohmann_json_serialize_enum_2.output"
```
See also
Version history
Added in version 3.4.0.