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98 lines
4.1 KiB
Markdown
98 lines
4.1 KiB
Markdown
# nlohmann::basic_json::to_cbor
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```
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// (1)
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static std::vector<std::uint8_t> to_cbor(const basic_json& j,
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const error_handler_t error_handler = error_handler_t::keep);
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// (2)
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static void to_cbor(const basic_json& j, detail::output_adapter<std::uint8_t> o,
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const error_handler_t error_handler = error_handler_t::keep);
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static void to_cbor(const basic_json& j, detail::output_adapter<char> o,
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const error_handler_t error_handler = error_handler_t::keep);
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```
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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.
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1. Returns a byte vector containing the CBOR serialization.
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1. Writes the CBOR serialization to an output adapter.
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The exact mapping and its limitations are described on a [dedicated page](https://json.nlohmann.me/features/binary_formats/cbor/index.md).
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## Parameters
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`j` (in) : JSON value to serialize
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`o` (in) : output adapter to write serialization to
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`error_handler` (in) : how to treat a string or object key in `j` that is not valid UTF-8; see [`error_handler_t`](https://json.nlohmann.me/api/basic_json/error_handler_t/index.md). 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`](https://json.nlohmann.me/api/basic_json/dump/index.md) would. If [`JSON_STRICT_BINARY_UTF8`](https://json.nlohmann.me/api/macros/json_strict_binary_utf8/index.md) is enabled, the default is `strict` instead.
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## Return value
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1. CBOR serialization as a byte vector
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1. (none)
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## Exception safety
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Strong guarantee: if an exception is thrown, there are no changes in the JSON value.
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## Exceptions
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- Throws [type_error.316](https://json.nlohmann.me/home/exceptions/#jsonexceptiontype_error316) 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`](https://json.nlohmann.me/api/macros/json_strict_binary_utf8/index.md) is enabled)
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## Complexity
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Linear in the size of the JSON value `j`.
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## Examples
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Example
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The example shows the serialization of a JSON value to a byte vector in CBOR format.
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```
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#include <iostream>
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#include <iomanip>
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#include <nlohmann/json.hpp>
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using json = nlohmann::json;
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using namespace nlohmann::literals;
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int main()
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{
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// create a JSON value
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json j = R"({"compact": true, "schema": 0})"_json;
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// serialize it to CBOR
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std::vector<std::uint8_t> v = json::to_cbor(j);
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// print the vector content
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for (auto& byte : v)
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{
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std::cout << "0x" << std::hex << std::setw(2) << std::setfill('0') << (int)byte << " ";
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}
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std::cout << std::endl;
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}
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```
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Output:
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```
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0xa2 0x67 0x63 0x6f 0x6d 0x70 0x61 0x63 0x74 0xf5 0x66 0x73 0x63 0x68 0x65 0x6d 0x61 0x00
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```
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## See also
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- [from_cbor](https://json.nlohmann.me/api/basic_json/from_cbor/index.md) create a JSON value from an input in CBOR format
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- [to_msgpack](https://json.nlohmann.me/api/basic_json/to_msgpack/index.md) create a MessagePack serialization of a JSON value
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- [to_bson](https://json.nlohmann.me/api/basic_json/to_bson/index.md) create a BSON serialization of a JSON value
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- [to_ubjson](https://json.nlohmann.me/api/basic_json/to_ubjson/index.md) create a UBJSON serialization of a JSON value
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- [to_bjdata](https://json.nlohmann.me/api/basic_json/to_bjdata/index.md) create a BJData serialization of a JSON value
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- [to_bon8](https://json.nlohmann.me/api/basic_json/to_bon8/index.md) create a BON8 serialization of a JSON value
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## Version history
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- Added in version 2.0.9.
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- Compact representation of floating-point numbers added in version 3.8.0.
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- Added `error_handler` parameter in version 3.13.0 unreleased. 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`](https://json.nlohmann.me/api/macros/json_strict_binary_utf8/index.md) is enabled) throws `type_error.316`.
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