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93 lines
3.2 KiB
Markdown
93 lines
3.2 KiB
Markdown
# nlohmann::basic_json::to_msgpack
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```
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// (1)
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static std::vector<std::uint8_t> to_msgpack(const basic_json& j);
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// (2)
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static void to_msgpack(const basic_json& j, detail::output_adapter<std::uint8_t> o);
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static void to_msgpack(const basic_json& j, detail::output_adapter<char> o);
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```
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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.
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1. Returns a byte vector containing the MessagePack serialization.
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1. Writes the MessagePack 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/messagepack/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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## Return value
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1. MessagePack 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 [`out_of_range.412`](https://json.nlohmann.me/home/exceptions/#jsonexceptionout_of_range412) 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"`
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- Throws [`out_of_range.415`](https://json.nlohmann.me/home/exceptions/#jsonexceptionout_of_range415) 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)"`
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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 MessagePack 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 MessagePack
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std::vector<std::uint8_t> v = json::to_msgpack(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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0x82 0xa7 0x63 0x6f 0x6d 0x70 0x61 0x63 0x74 0xc3 0xa6 0x73 0x63 0x68 0x65 0x6d 0x61 0x00
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```
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## See also
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- [from_msgpack](https://json.nlohmann.me/api/basic_json/from_msgpack/index.md) create a JSON value from an input in MessagePack format
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- [to_cbor](https://json.nlohmann.me/api/basic_json/to_cbor/index.md) create a CBOR 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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- Throws `out_of_range.412` and `out_of_range.415` since version 3.13.0.
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