json/api/basic_json/from_ubjson/index.md

nlohmann::basic_json::from_ubjson

// (1)
template<typename InputType>
static basic_json from_ubjson(InputType&& i,
                              const bool strict = true,
                              const bool allow_exceptions = true);
// (2)
template<typename IteratorType>
static basic_json from_ubjson(IteratorType first, IteratorType last,
                              const bool strict = true,
                              const bool allow_exceptions = true);

Deserializes a given input to a JSON value using the UBJSON (Universal Binary JSON) serialization format.

1. Reads from a compatible input.
2. Reads from an iterator range.

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

Template parameters

InputType : A compatible input, for instance:

- an `std::istream` object
- a `FILE` pointer
- a C-style array of characters
- a pointer to a null-terminated string of single byte characters
- an object `obj` for which `begin(obj)` and `end(obj)` produces a valid pair of iterators.

IteratorType : a compatible iterator type

Parameters

i (in) : an input in UBJSON format convertible to an input adapter

first (in) : iterator to the start of the input

last (in) : iterator to the end of the input

strict (in) : whether to expect the input to be consumed until EOF (true by default)

allow_exceptions (in) : whether to throw exceptions in case of a parse error (optional, true by default)

Return value

deserialized JSON value; in case of a parse error and allow_exceptions set to false, the return value will be value_t::discarded. The latter can be checked with is_discarded.

Exception safety

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

Exceptions

• Throws parse_error.110 if the given input ends prematurely or the end of the file was not reached when strict was set to true
• Throws parse_error.112 if a parse error occurs
• Throws parse_error.113 if a string could not be parsed successfully
• Throws out_of_range.408 if the size of an optimized container or n-dimensional array cannot be represented by std::size_t

Complexity

Linear in the size of the input.

Examples

Example

The example shows the deserialization of a byte vector in UBJSON format to a JSON value.

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

using json = nlohmann::json;

int main()
{
    // create byte vector
    std::vector<std::uint8_t> v = {0x7B, 0x69, 0x07, 0x63, 0x6F, 0x6D, 0x70, 0x61,
                                   0x63, 0x74, 0x54, 0x69, 0x06, 0x73, 0x63, 0x68,
                                   0x65, 0x6D, 0x61, 0x69, 0x00, 0x7D
                                  };

    // deserialize it with UBJSON
    json j = json::from_ubjson(v);

    // print the deserialized JSON value
    std::cout << std::setw(2) << j << std::endl;
}

Output:

{
  "compact": true,
  "schema": 0
}

See also

• to_ubjson create a UBJSON serialization of a JSON value
• from_cbor create a JSON value from an input in CBOR format
• from_msgpack create a JSON value from an input in MessagePack format
• from_bson create a JSON value from an input in BSON format
• from_bjdata create a JSON value from an input in BJData format

Version history

• Added in version 3.1.0.
• Added allow_exceptions parameter in version 3.2.0.

Deprecation

• Overload (2) replaces calls to from_ubjson with a pointer and a length as first two parameters, which has been deprecated in version 3.8.0. This overload will be removed in version 4.0.0. Please replace all calls like from_ubjson(ptr, len, ...); with from_ubjson(ptr, ptr+len, ...);.
• Overload (2) replaces calls to from_ubjson with a pair of iterators as their first parameter, which has been deprecated in version 3.8.0. This overload will be removed in version 4.0.0. Please replace all calls like from_ubjson({ptr, ptr+len}, ...); with from_ubjson(ptr, ptr+len, ...);.

You should be warned by your compiler with a -Wdeprecated-declarations warning if you are using a deprecated function.