nlohmann::basic_json::from_bson

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

Deserializes a given input to a JSON value using the BSON (Binary JSON) 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 BSON 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 input was not reached when strict was set to true
• Throws parse_error.112 if a parse error occurs (e.g., an invalid string or byte array length)
• Throws parse_error.114 if an unsupported BSON record type is encountered

Complexity

Linear in the size of the input.

Examples

Example

The example shows the deserialization of a byte vector in BSON 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 = {0x1b, 0x00, 0x00, 0x00, 0x08, 0x63, 0x6f, 0x6d,
                                   0x70, 0x61, 0x63, 0x74, 0x00, 0x01, 0x10, 0x73,
                                   0x63, 0x68, 0x65, 0x6d, 0x61, 0x00, 0x00, 0x00,
                                   0x00, 0x00, 0x00
                                  };

    // deserialize it with BSON
    json j = json::from_bson(v);

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

Output:

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

See also

• BSON specification
• to_bson for the analogous serialization
• from_cbor for the related CBOR format
• from_msgpack for the related MessagePack format
• from_ubjson for the related UBJSON format
• from_bjdata for the related BJData format

Version history

• Added in version 3.4.0.
• Extended container support (1) to include types with lvalue-only ADL begin/end (matching std::begin/std::end semantics) in version 3.13.0.
• Extended overload (2) to accept heterogeneous iterator+sentinel pairs (C++20 ranges support) in version 3.13.0.

Deprecation

• Overload (2) replaces calls to from_bson 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_bson(ptr, len, ...); with from_bson(ptr, ptr+len, ...);.
• Overload (2) replaces calls to from_bson 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_bson({ptr, ptr+len}, ...); with from_bson(ptr, ptr+len, ...);.

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