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# 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>
    static basic_json from_bson(IteratorType first, IteratorType 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.

The exact mapping and its limitations is 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 BSON format convertible to an input adapter
`first` (in)
  iterator to start of the input
`last` (in)
  iterator to 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.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

## Version history

- Added in version 3.4.0.

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.

Last update: May 1, 2022
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