deploy: 7c9208bfb3

2026-07-09 12:05:10 +00:00 · 2026-07-08 18:19:46 +00:00
parent 9a231845c2
commit 279d757031
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+# nlohmann::basic_json::to_bjdata
+
+```
+// (1)
+static std::vector<std::uint8_t> to_bjdata(const basic_json& j,
+                                           const bool use_size = false,
+                                           const bool use_type = false,
+                                           const bjdata_version_t version = bjdata_version_t::draft2);
+
+// (2)
+static void to_bjdata(const basic_json& j, detail::output_adapter<std::uint8_t> o,
+                      const bool use_size = false, const bool use_type = false,
+                      const bjdata_version_t version = bjdata_version_t::draft2);
+static void to_bjdata(const basic_json& j, detail::output_adapter<char> o,
+                      const bool use_size = false, const bool use_type = false,
+                      const bjdata_version_t version = bjdata_version_t::draft2);
+```
+
+Serializes a given JSON value `j` to a byte vector using the BJData (Binary JData) serialization format. BJData aims to be more compact than JSON itself, yet more efficient to parse.
+
+1. Returns a byte vector containing the BJData serialization.
+1. Writes the BJData serialization to an output adapter.
+
+The exact mapping and its limitations are described on a [dedicated page](https://json.nlohmann.me/features/binary_formats/bjdata/index.md).
+
+## 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.
+
+`version` (in) : which version of BJData to use (see note on "Binary values" on [BJData](https://json.nlohmann.me/features/binary_formats/bjdata/index.md)); optional, `bjdata_version_t::draft2` by default.
+
+## Return value
+
+1. BJData serialization as byte vector
+1. (none)
+
+## 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 BJData format.
+
+```
+#include <iostream>
+#include <iomanip>
+#include <nlohmann/json.hpp>
+
+using json = nlohmann::json;
+using namespace nlohmann::literals;
+
+// function to print BJData'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 BJData
+    std::vector<std::uint8_t> v = json::to_bjdata(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 BJData using default representation
+    std::vector<std::uint8_t> v_array = json::to_bjdata(array);
+    // serialize it to BJData using size optimization
+    std::vector<std::uint8_t> v_array_size = json::to_bjdata(array, true);
+    // serialize it to BJData using type optimization
+    std::vector<std::uint8_t> v_array_size_and_type = json::to_bjdata(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
+```
+
+## See also
+
+- [from_bjdata](https://json.nlohmann.me/api/basic_json/from_bjdata/index.md) create a JSON value from an input in BJData format
+- [to_cbor](https://json.nlohmann.me/api/basic_json/to_cbor/index.md) create a CBOR serialization of a JSON value
+- [to_msgpack](https://json.nlohmann.me/api/basic_json/to_msgpack/index.md) create a MessagePack serialization of a JSON value
+- [to_bson](https://json.nlohmann.me/api/basic_json/to_bson/index.md) create a BSON serialization of a JSON value
+- [to_ubjson](https://json.nlohmann.me/api/basic_json/to_ubjson/index.md) create a UBJSON serialization of a JSON value
+
+## Version history
+
+- Added in version 3.11.0.
+- BJData version parameter (for draft3 binary encoding) added in version 3.12.0.