JSON for Modern C++  3.7.2

◆ to_cbor() [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>
static std::vector<uint8_t> nlohmann::basic_json::to_cbor ( const basic_json j)

Serializes a given JSON value j to a byte vector using the CBOR (Concise Binary Object Representation) serialization format. CBOR 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 CBOR types according to the CBOR specification (RFC 7049):

JSON value type value/range CBOR type first byte
null null Null 0xF6
boolean true True 0xF5
boolean false False 0xF4
number_integer -9223372036854775808..-2147483649 Negative integer (8 bytes follow) 0x3B
number_integer -2147483648..-32769 Negative integer (4 bytes follow) 0x3A
number_integer -32768..-129 Negative integer (2 bytes follow) 0x39
number_integer -128..-25 Negative integer (1 byte follow) 0x38
number_integer -24..-1 Negative integer 0x20..0x37
number_integer 0..23 Integer 0x00..0x17
number_integer 24..255 Unsigned integer (1 byte follow) 0x18
number_integer 256..65535 Unsigned integer (2 bytes follow) 0x19
number_integer 65536..4294967295 Unsigned integer (4 bytes follow) 0x1A
number_integer 4294967296..18446744073709551615 Unsigned integer (8 bytes follow) 0x1B
number_unsigned 0..23 Integer 0x00..0x17
number_unsigned 24..255 Unsigned integer (1 byte follow) 0x18
number_unsigned 256..65535 Unsigned integer (2 bytes follow) 0x19
number_unsigned 65536..4294967295 Unsigned integer (4 bytes follow) 0x1A
number_unsigned 4294967296..18446744073709551615 Unsigned integer (8 bytes follow) 0x1B
number_float any value Double-Precision Float 0xFB
string length: 0..23 UTF-8 string 0x60..0x77
string length: 23..255 UTF-8 string (1 byte follow) 0x78
string length: 256..65535 UTF-8 string (2 bytes follow) 0x79
string length: 65536..4294967295 UTF-8 string (4 bytes follow) 0x7A
string length: 4294967296..18446744073709551615 UTF-8 string (8 bytes follow) 0x7B
array size: 0..23 array 0x80..0x97
array size: 23..255 array (1 byte follow) 0x98
array size: 256..65535 array (2 bytes follow) 0x99
array size: 65536..4294967295 array (4 bytes follow) 0x9A
array size: 4294967296..18446744073709551615 array (8 bytes follow) 0x9B
object size: 0..23 map 0xA0..0xB7
object size: 23..255 map (1 byte follow) 0xB8
object size: 256..65535 map (2 bytes follow) 0xB9
object size: 65536..4294967295 map (4 bytes follow) 0xBA
object size: 4294967296..18446744073709551615 map (8 bytes follow) 0xBB
The mapping is complete in the sense that any JSON value type can be converted to a CBOR value.
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.
The following CBOR types are not used in the conversion:
  • byte strings (0x40..0x5F)
  • UTF-8 strings terminated by "break" (0x7F)
  • arrays terminated by "break" (0x9F)
  • maps terminated by "break" (0xBF)
  • date/time (0xC0..0xC1)
  • bignum (0xC2..0xC3)
  • decimal fraction (0xC4)
  • bigfloat (0xC5)
  • tagged items (0xC6..0xD4, 0xD8..0xDB)
  • expected conversions (0xD5..0xD7)
  • simple values (0xE0..0xF3, 0xF8)
  • undefined (0xF7)
  • half and single-precision floats (0xF9-0xFA)
  • break (0xFF)
[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 CBOR format.
1 #include <iostream>
2 #include <iomanip>
3 #include <nlohmann/json.hpp>
5 using json = nlohmann::json;
7 int main()
8 {
9  // create a JSON value
10  json j = R"({"compact": true, "schema": 0})"_json;
12  // serialize it to CBOR
13  std::vector<uint8_t> v = json::to_cbor(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;
21 }

Output (play with this example online):
0xa2 0x67 0x63 0x6f 0x6d 0x70 0x61 0x63 0x74 0xf5 0x66 0x73 0x63 0x68 0x65 0x6d 0x61 0x00 
The example code above can be translated with
g++ -std=c++11 -Isingle_include doc/examples/to_cbor.cpp -o to_cbor 
See also
from_cbor(detail::input_adapter&&, const bool, const bool) for the analogous deserialization
to_msgpack(const basic_json&) for the related MessagePack format
to_ubjson(const basic_json&, const bool, const bool) for the related UBJSON format
version 2.0.9

Definition at line 21130 of file json.hpp.

static std::vector< uint8_t > to_cbor(const basic_json &j)
create a CBOR serialization of a given JSON value
Definition: json.hpp:21130
basic_json<> json
default JSON class
Definition: json.hpp:2445