Skip to content


// (1)
static std::vector<std::uint8_t> to_bson(const basic_json& j);

// (2)
static void to_bson(const basic_json& j, detail::output_adapter<std::uint8_t> o);
static void to_bson(const basic_json& j, detail::output_adapter<char> o);

BSON (Binary JSON) is a binary format in which zero or more ordered key/value pairs are stored as a single entity (a so-called document).

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

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


j (in)
JSON value to serialize
o (in)
output adapter to write serialization to

Return value

  1. BSON serialization as byte vector
  2. (none)

Exception safety

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


Linear in the size of the JSON value j.



The example shows the serialization of a JSON value to a byte vector in BSON format.

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

using json = nlohmann::json;
using namespace nlohmann::literals;

int main()
    // create a JSON value
    json j = R"({"compact": true, "schema": 0})"_json;

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

    // print the vector content
    for (auto& byte : v)
        std::cout << "0x" << std::hex << std::setw(2) << std::setfill('0') << (int)byte << " ";
    std::cout << std::endl;


0x1b 0x00 0x00 0x00 0x08 0x63 0x6f 0x6d 0x70 0x61 0x63 0x74 0x00 0x01 0x10 0x73 0x63 0x68 0x65 0x6d 0x61 0x00 0x00 0x00 0x00 0x00 0x00 

Version history

  • Added in version 3.4.0.

Last update: May 1, 2022