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# nlohmann::basic_json::to_ubjson

    // (1)
    static std::vector<std::uint8_t> to_ubjson(const basic_json& j,
                                               const bool use_size = false,
                                               const bool use_type = false);

    // (2)
    static void to_ubjson(const basic_json& j, detail::output_adapter<std::uint8_t> o,
                          const bool use_size = false, const bool use_type = false);
    static void to_ubjson(const basic_json& j, detail::output_adapter<char> o,
                          const bool use_size = false, const bool use_type = false);

Serializes a given JSON value `j` to a byte vector using the UBJSON (Universal Binary JSON) serialization format. UBJSON aims to be more compact than JSON itself, yet more efficient to parse.

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

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

## Parameters

`j` (in)
  JSON value to serialize
`o` (in)
  output adapter to write serialization to
`use_size` (in)
  whether to add size annotations to container types; optional, `false` by default.
`use_type` (in)
  whether to add type annotations to container types (must be combined with `use_size = true`); optional, `false` by default.

## Return value

1. UBJSON serialization as byte vector
2. /

## Exception safety

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

## 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 UBJSON format.

    #include <iostream>
    #include <iomanip>
    #include <nlohmann/json.hpp>

    using json = nlohmann::json;

    // function to print UBJSON's diagnostic format
    void print_byte(uint8_t byte)
    {
        if (32 < byte and byte < 128)
        {
            std::cout << (char)byte;
        }
        else
        {
            std::cout << (int)byte;
        }
    }

    int main()
    {
        // create a JSON value
        json j = R"({"compact": true, "schema": false})"_json;

        // serialize it to UBJSON
        std::vector<std::uint8_t> v = json::to_ubjson(j);

        // print the vector content
        for (auto& byte : v)
        {
            print_byte(byte);
        }
        std::cout << std::endl;

        // create an array of numbers
        json array = {1, 2, 3, 4, 5, 6, 7, 8};

        // serialize it to UBJSON using default representation
        std::vector<std::uint8_t> v_array = json::to_ubjson(array);
        // serialize it to UBJSON using size optimization
        std::vector<std::uint8_t> v_array_size = json::to_ubjson(array, true);
        // serialize it to UBJSON using type optimization
        std::vector<std::uint8_t> v_array_size_and_type = json::to_ubjson(array, true, true);

        // print the vector contents
        for (auto& byte : v_array)
        {
            print_byte(byte);
        }
        std::cout << std::endl;

        for (auto& byte : v_array_size)
        {
            print_byte(byte);
        }
        std::cout << std::endl;

        for (auto& byte : v_array_size_and_type)
        {
            print_byte(byte);
        }
        std::cout << std::endl;
    }

Output:

    {i7compactTi6schemaF}
    [i1i2i3i4i5i6i7i8]
    [#i8i1i2i3i4i5i6i7i8
    [$i#i812345678

## Version history

- Added in version 3.1.0.

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