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140 lines
3.9 KiB
Markdown
140 lines
3.9 KiB
Markdown
# <small>nlohmann::basic_json::</small>to_bon8
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```cpp
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// (1)
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static std::vector<std::uint8_t> to_bon8(const basic_json& j);
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// (2)
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static void to_bon8(const basic_json& j, detail::output_adapter<std::uint8_t> o);
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static void to_bon8(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 BON8 (Binary Object Notation 8) serialization format. BON8
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is a compact binary serialization format that stores strings as UTF-8 without a length prefix.
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1. Returns a byte vector containing the BON8 serialization.
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2. Writes the BON8 serialization to an output adapter.
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The exact mapping and its limitations are described on a [dedicated page](../../features/binary_formats/bon8.md).
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## Parameters
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`j` (in)
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: JSON value to serialize
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`o` (in)
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: output adapter to write serialization to
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## Return value
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1. BON8 serialization as a byte vector
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2. (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 `j`, which is never modified.
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With (2), the bytes written before the exception remain in the output adapter.
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## Exceptions
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- Throws [out_of_range.407](../../home/exceptions.md#jsonexceptionout_of_range407) if `j` contains an unsigned integer
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above 9223372036854775807, which BON8 cannot represent
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- Throws [type_error.316](../../home/exceptions.md#jsonexceptiontype_error316) if `j` contains a string that is not
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valid UTF-8
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- Throws [type_error.321](../../home/exceptions.md#jsonexceptiontype_error321) if `j` or a value nested in it is
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discarded; example: `"cannot serialize discarded value to BON8"`
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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 "Example: serialize a JSON value to BON8"
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The example shows the serialization of a JSON value to a byte vector in BON8 format.
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```cpp
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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, "format": "BON8", "schema": 0})"_json;
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// serialize it to BON8
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std::vector<std::uint8_t> v = json::to_bon8(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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```json
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0x89 0x63 0x6f 0x6d 0x70 0x61 0x63 0x74 0xf9 0x66 0x6f 0x72 0x6d 0x61 0x74 0xff 0x42 0x4f 0x4e 0x38 0xff 0x73 0x63 0x68 0x65 0x6d 0x61 0x90
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```
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??? example "Example: type_error.316 exception"
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The example shows how serializing a string that is not valid UTF-8 throws an exception, because BON8 stores strings
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as UTF-8.
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```cpp
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#include <iostream>
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#include <nlohmann/json.hpp>
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using json = nlohmann::json;
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int main()
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{
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// create a JSON string that is not valid UTF-8
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std::string invalid_utf8;
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invalid_utf8.push_back(static_cast<char>(0xFF));
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json j = invalid_utf8;
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// exception type_error.316
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try
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{
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json::to_bon8(j);
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}
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catch (const json::type_error& e)
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{
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std::cout << e.what() << '\n';
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}
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}
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```
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Output:
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```json
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[json.exception.type_error.316] invalid UTF-8 byte at index 0: 0xFF
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```
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## See also
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- [from_bon8](from_bon8.md) create a JSON value from an input in BON8 format
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- [to_cbor](to_cbor.md) create a CBOR serialization of a JSON value
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- [to_msgpack](to_msgpack.md) create a MessagePack serialization of a JSON value
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- [to_bson](to_bson.md) create a BSON serialization of a JSON value
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- [to_ubjson](to_ubjson.md) create a UBJSON serialization of a JSON value
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- [to_bjdata](to_bjdata.md) create a BJData serialization of a JSON value
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## Version history
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- Added in version 3.13.0.
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