JSON for Modern C++ 3.10.4

◆ to_msgpack() [1/3]

template<template< typename U, typename V, typename... Args > class ObjectType = std::map, template< typename U, typename... Args > class ArrayType = std::vector, class StringType = std::string, class BooleanType = bool, class NumberIntegerType = std::int64_t, class NumberUnsignedType = std::uint64_t, class NumberFloatType = double, template< typename U > class AllocatorType = std::allocator, template< typename T, typename SFINAE=void > class JSONSerializer = adl_serializer, class BinaryType = std::vector<std::uint8_t>>
static std::vector< std::uint8_t > nlohmann::basic_json< ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer, BinaryType >::to_msgpack ( const basic_json< ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer, BinaryType > &  j)

Serializes a given JSON value j to a byte vector using the MessagePack serialization format. MessagePack is a binary serialization format which aims to be more compact than JSON itself, yet more efficient to parse.

The library uses the following mapping from JSON values types to MessagePack types according to the MessagePack specification:

JSON value type value/range MessagePack type first byte
null null nil 0xC0
boolean true true 0xC3
boolean false false 0xC2
number_integer -9223372036854775808..-2147483649 int64 0xD3
number_integer -2147483648..-32769 int32 0xD2
number_integer -32768..-129 int16 0xD1
number_integer -128..-33 int8 0xD0
number_integer -32..-1 negative fixint 0xE0..0xFF
number_integer 0..127 positive fixint 0x00..0x7F
number_integer 128..255 uint 8 0xCC
number_integer 256..65535 uint 16 0xCD
number_integer 65536..4294967295 uint 32 0xCE
number_integer 4294967296..18446744073709551615 uint 64 0xCF
number_unsigned 0..127 positive fixint 0x00..0x7F
number_unsigned 128..255 uint 8 0xCC
number_unsigned 256..65535 uint 16 0xCD
number_unsigned 65536..4294967295 uint 32 0xCE
number_unsigned 4294967296..18446744073709551615 uint 64 0xCF
number_float any value representable by a float float 32 0xCA
number_float any value NOT representable by a float float 64 0xCB
string length: 0..31 fixstr 0xA0..0xBF
string length: 32..255 str 8 0xD9
string length: 256..65535 str 16 0xDA
string length: 65536..4294967295 str 32 0xDB
array size: 0..15 fixarray 0x90..0x9F
array size: 16..65535 array 16 0xDC
array size: 65536..4294967295 array 32 0xDD
object size: 0..15 fix map 0x80..0x8F
object size: 16..65535 map 16 0xDE
object size: 65536..4294967295 map 32 0xDF
binary size: 0..255 bin 8 0xC4
binary size: 256..65535 bin 16 0xC5
binary size: 65536..4294967295 bin 32 0xC6
The mapping is complete in the sense that any JSON value type can be converted to a MessagePack value.
The following values can not be converted to a MessagePack value:
  • strings with more than 4294967295 bytes
  • byte strings with more than 4294967295 bytes
  • arrays with more than 4294967295 elements
  • objects with more than 4294967295 elements
Any MessagePack output created to_msgpack can be successfully parsed by from_msgpack.
If NaN or Infinity are stored inside a JSON number, they are serialized properly. This behavior differs from the dump() function which serializes NaN or Infinity to null.
[in]jJSON value to serialize
MessagePack serialization as byte vector
Linear in the size of the JSON value j.
The example shows the serialization of a JSON value to a byte vector in MessagePack format.
1#include <iostream>
2#include <iomanip>
3#include <nlohmann/json.hpp>
5using json = nlohmann::json;
7int main()
9 // create a JSON value
10 json j = R"({"compact": true, "schema": 0})"_json;
12 // serialize it to MessagePack
13 std::vector<uint8_t> v = json::to_msgpack(j);
15 // print the vector content
16 for (auto& byte : v)
17 {
18 std::cout << "0x" << std::hex << std::setw(2) << std::setfill('0') << (int)byte << " ";
19 }
20 std::cout << std::endl;
static std::vector< std::uint8_t > to_msgpack(const basic_json &j)
create a MessagePack serialization of a given JSON value
Definition: json.hpp:24932
basic_json<> json
default JSON class
Definition: json.hpp:3472

Output (play with this example online):
0x82 0xa7 0x63 0x6f 0x6d 0x70 0x61 0x63 0x74 0xc3 0xa6 0x73 0x63 0x68 0x65 0x6d 0x61 0x00 
The example code above can be translated with
g++ -std=c++11 -Isingle_include doc/examples/to_msgpack.cpp -o to_msgpack 
See also
see from_msgpack for the analogous deserialization
see to_cbor(const basic_json& for the related CBOR format
see to_ubjson(const basic_json&, const bool, const bool) for the related UBJSON format
version 2.0.9

Definition at line 24932 of file json.hpp.