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nlohmann committed 2026-10-12 07:35:31 +00:00
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@@ -56,13 +56,67 @@ inline void from_json(const BasicJsonType& j, type& e);
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_strict.cpp"
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
namespace ns
{
enum TaskState
{
TS_STOPPED,
TS_RUNNING,
TS_COMPLETED,
TS_INVALID = -1
};
NLOHMANN_JSON_SERIALIZE_ENUM_STRICT(TaskState,
{
{ TS_INVALID, nullptr },
{ TS_STOPPED, "stopped" },
{ TS_RUNNING, "running" },
{ TS_COMPLETED, "completed" }
})
enum class Color
{
red, green, blue, unknown
};
NLOHMANN_JSON_SERIALIZE_ENUM_STRICT(Color,
{
{ Color::unknown, "unknown" }, { Color::red, "red" },
{ Color::green, "green" }, { Color::blue, "blue" }
})
} // namespace ns
int main()
{
// serialization
json j_stopped = ns::TS_STOPPED;
json j_red = ns::Color::red;
std::cout << "ns::TS_STOPPED -> " << j_stopped
<< ", ns::Color::red -> " << j_red << std::endl;
// deserialization
json j_running = "running";
json j_blue = "blue";
auto running = j_running.get<ns::TaskState>();
auto blue = j_blue.get<ns::Color>();
std::cout << j_running << " -> " << running
<< ", " << j_blue << " -> " << static_cast<int>(blue) << std::endl;
}
```
Output:
```json
--8<-- "examples/nlohmann_json_serialize_enum_strict.output"
ns::TS_STOPPED -> "stopped", ns::Color::red -> "red"
"running" -> 1, "blue" -> 2
```
??? example "Example: Multiple conversions for one enumerator"
@@ -72,13 +126,49 @@ inline void from_json(const BasicJsonType& j, type& e);
alternative *deserialization* from `"rot"` to `Color::red`.
```cpp hl_lines="17"
--8<-- "examples/nlohmann_json_serialize_enum_strict_2.cpp"
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
namespace ns
{
enum class Color
{
red, green, blue, unknown
};
NLOHMANN_JSON_SERIALIZE_ENUM_STRICT(Color,
{
{ Color::unknown, "unknown" }, { Color::red, "red" },
{ Color::green, "green" }, { Color::blue, "blue" },
{ Color::red, "rot" } // a second conversion for Color::red
})
}
int main()
{
// serialization
json j_red = ns::Color::red;
std::cout << static_cast<int>(ns::Color::red) << " -> " << j_red << std::endl;
// deserialization
json j_rot = "rot";
auto rot = j_rot.get<ns::Color>();
auto red = j_red.get<ns::Color>();
std::cout << j_rot << " -> " << static_cast<int>(rot) << std::endl;
std::cout << j_red << " -> " << static_cast<int>(red) << std::endl;
}
```
Output:
```json
--8<-- "examples/nlohmann_json_serialize_enum_strict_2.output"
0 -> "red"
"rot" -> 0
"red" -> 0
```
??? example "Example: exceptions on invalid serialization"
@@ -89,12 +179,67 @@ inline void from_json(const BasicJsonType& j, type& e);
value so also causes an exception when deserialization is attempted.
```cpp hl_lines="14 32 33 43 44 45"
--8<-- "examples/nlohmann_json_serialize_enum_strict_err.cpp"
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
namespace ns
{
enum class Color
{
red,
green,
blue,
unknown // not mapped in JSON_SERIALIZE_ENUM_STRICT
};
NLOHMANN_JSON_SERIALIZE_ENUM_STRICT(Color,
{
{Color::red, "red"},
{Color::green, "green"},
{Color::blue, "blue"}
})
} // namespace ns
int main()
{
// invalid serialization
try
{
// ns::color::unknown was not mapped in macro
json invalid_serialization = ns::Color::unknown;
}
catch (const json::exception e)
{
std::cout << "deserialization failed: " << e.what() << std::endl;
}
// invalid deserialization
try
{
// what does not map to an enum
json invalid_deserialization("what");
ns::Color color = invalid_deserialization.get<ns::Color>();
}
catch (const json::exception e)
{
std::cout << "deserialization failed: " << e.what() << std::endl;
}
return 0;
}
```
Output:
```json
--8<-- "examples/nlohmann_json_serialize_enum_strict_err.output"
deserialization failed: [json.exception.out_of_range.410] enum value out of range for Color
deserialization failed: [json.exception.out_of_range.410] enum value out of range for Color: "what"
```
## See also