json/docs/mkdocs/docs/api/basic_json/to_cbor.md

nlohmann::basic_json::to_cbor

// (1)
static std::vector<std::uint8_t> to_cbor(const basic_json& j,
                                          const error_handler_t error_handler = error_handler_t::keep);

// (2)
static void to_cbor(const basic_json& j, detail::output_adapter<std::uint8_t> o,
                     const error_handler_t error_handler = error_handler_t::keep);
static void to_cbor(const basic_json& j, detail::output_adapter<char> o,
                     const error_handler_t error_handler = error_handler_t::keep);

Serializes a given JSON value j to a byte vector using the CBOR (Concise Binary Object Representation) serialization format. CBOR 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 CBOR serialization.
2. Writes the CBOR 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

error_handler (in)

how to treat a string or object key in j that is not valid UTF-8; see error_handler_t. The default, keep, writes the ill-formed bytes to the output as is, as every version of to_cbor did before this parameter was added; strict throws; replace/ignore sanitize it the same way dump would. If JSON_STRICT_BINARY_UTF8 is enabled, the default is strict instead.

Return value

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

Exception safety

Strong guarantee: if an exception is thrown, there are no changes in the JSON value. Bytes that were already written to the output adapter are not taken back.

Exceptions

• Throws out_of_range.407 if j contains an integer outside [-2^64, 2^64-1], which is only possible with a number type wider than 64 bits; example: "integer number 18446744073709551616 cannot be represented by CBOR as it does not fit [-2^64, 2^64-1]"
• Throws type_error.316 if a string or object key in j is not valid UTF-8 and error_handler is strict (the default only if JSON_STRICT_BINARY_UTF8 is enabled)
• Throws type_error.321 if j or a value nested in it is discarded; example: "cannot serialize discarded value to CBOR"

Complexity

Linear in the size of the JSON value j.

Examples

??? example

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

Output:

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

See also

• CBOR - the format, its byte layout and how values are mapped
• Binary formats - overview and comparison of the supported binary formats
• Binary values - how binary values and subtypes are handled
• from_cbor - create a JSON value from an input in CBOR format
• to_msgpack - create a MessagePack 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.
• Compact representation of floating-point numbers added in version 3.8.0.
• Added error_handler parameter in version 3.13.0. Its default, keep, writes the bytes of a string or object key that is not valid UTF-8 unchanged, as before; strict (the default if JSON_STRICT_BINARY_UTF8 is enabled) throws type_error.316.
• Throws type_error.321 for a discarded value since version 3.13.0; previously, a discarded value nested in an array or object was silently skipped, producing invalid CBOR.
• Throws out_of_range.407 for integers that do not fit 64 bits since version 3.13.0; previously, integers of a number type wider than 64 bits were silently truncated.