nlohmann::basic_json::from_bon8

// (1)
template<typename InputType>
static basic_json from_bon8(InputType&& i,
                            const bool strict = true,
                            const bool allow_exceptions = true);
// (2)
template<typename IteratorType, typename SentinelType = IteratorType>
static basic_json from_bon8(IteratorType first, SentinelType last,
                            const bool strict = true,
                            const bool allow_exceptions = true);

Deserializes a given input to a JSON value using the BON8 (Binary Object Notation 8) serialization format.

1. Reads from a compatible input.
2. Reads from an iterator range, or an iterator and a sentinel of a different type (C++20 ranges support).

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
- a container `obj` for which `begin(obj)` and `end(obj)` produce a valid pair of iterators
  (as found via ADL or member functions, with semantics compatible to `std::begin` and `std::end`)

IteratorType : a compatible iterator type

SentinelType : defaults to IteratorType; may be a different type comparable to IteratorType via operator!=, for instance.

- a custom sentinel type for C++20 ranges
- `std::default_sentinel_t`, when `IteratorType` is `std::counted_iterator`

Parameters

i (in) : an input in BON8 format convertible to an input adapter

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

last (in) : iterator to the end of the input, or a sentinel value that compares equal to the end iterator with operator!=

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, for instance an invalid byte, a string that is not valid UTF-8, or an object key that is not a string

The UTF-8 validity of strings is always checked, independent of JSON_STRICT_BINARY_UTF8, because the end of a BON8 string is determined from its encoding. Duplicate object keys are accepted; the last value wins (see BON8).

Complexity

Linear in the size of the input.

Examples

Example

The example shows the deserialization of a byte vector in BON8 format to a JSON value.

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

using nlohmann::json;

int main()
{
    // create byte vector
    std::vector<std::uint8_t> v = {0x89, 0x63, 0x6f, 0x6d, 0x70, 0x61, 0x63, 0x74,
                                   0xf9, 0x66, 0x6f, 0x72, 0x6d, 0x61, 0x74, 0xff,
                                   0x42, 0x4f, 0x4e, 0x38, 0xff, 0x73, 0x63, 0x68,
                                   0x65, 0x6d, 0x61, 0x90
                                  };

    // deserialize it with BON8
    json j = json::from_bon8(v);

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

Output:

{
  "compact": true,
  "format": "BON8",
  "schema": 0
}

See also

• to_bon8 create a BON8 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_ubjson create a JSON value from an input in UBJSON format
• from_bjdata create a JSON value from an input in BJData format

Version history

• Added in version 3.13.0 unreleased.

Deprecation

• Overload (2) replaces calls to from_bon8 with a pointer and a length as first two parameters, which has been deprecated in version 3.13.0 unreleased. In version 4.0.0 unreleased, this overload will be deleted (= delete) rather than removed. Please replace all calls like from_bon8(ptr, len, ...); with from_bon8(ptr, ptr+len, ...);.

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