json/api/basic_json/to_msgpack.md

nlohmann::basic_json::to_msgpack

// (1)
static std::vector<std::uint8_t> to_msgpack(const basic_json& j);

// (2)
static void to_msgpack(const basic_json& j, detail::output_adapter<std::uint8_t> o);
static void to_msgpack(const basic_json& j, detail::output_adapter<char> o);

Serializes a given JSON value j to a byte vector using the MessagePack serialization format. MessagePack is a binary serialization format that aims to be more compact than JSON itself, yet more efficient to parse.

1. Returns a byte vector containing the MessagePack serialization.
2. Writes the MessagePack serialization to an output adapter.

The exact mapping and its limitations are described on a dedicated page.

Parameters

j (in)

JSON value to serialize

o (in)

output adapter to write serialization to

Return value

1. MessagePack serialization as a byte vector
2. (none)

Exception safety

Strong guarantee: if an exception is thrown, there are no changes in the JSON value.

Exceptions

• Throws out_of_range.412 if the length of a string, binary value, array, or object exceeds 4294967295, the maximum MessagePack can store; example: "MessagePack length 4294967296 exceeds maximum of 4294967295"
• Throws out_of_range.415 if the subtype of a binary value exceeds 255, the maximum of the MessagePack ext type; example: "subtype 70000 is too large for the MessagePack ext type (max 255)"

Complexity

Linear in the size of the JSON value j.

Examples

??? example "Example: serialize a JSON value to MessagePack"

The example shows the serialization of a JSON value to a byte vector in MessagePack format.
 
```cpp
--8<-- "examples/to_msgpack.cpp"
```

Output:

```json
--8<-- "examples/to_msgpack.output"
```

??? example "Example: out_of_range.415 exception"

The example shows how serializing a binary value whose subtype exceeds 255 throws an exception, because the
MessagePack ext type stores the subtype in a single byte.

```cpp
--8<-- "examples/to_msgpack__exception.cpp"
```

Output:

```json
--8<-- "examples/to_msgpack__exception.output"
```

See also

• from_msgpack create a JSON value from an input in MessagePack format
• to_cbor create a CBOR serialization of a JSON value
• to_bson create a BSON serialization of a JSON value
• to_ubjson create a UBJSON serialization of a JSON value
• to_bjdata create a BJData serialization of a JSON value
• to_bon8 create a BON8 serialization of a JSON value

Version history

• Added in version 2.0.9.
• Throws out_of_range.412 and out_of_range.415 since version 3.13.0.
• Fixed in version 3.13.0 to serialize number_integer_t/number_unsigned_t pairs of different width correctly; before, integers could be serialized with the wrong value if number_integer_t was narrower than number_unsigned_t.