# <small>nlohmann::basic_json::</small>from_bjdata

```cpp
// (1)
template<typename InputType>
static basic_json from_bjdata(InputType&& i,
                              const bool strict = true,
                              const bool allow_exceptions = true,
                              const error_handler_t error_handler = error_handler_t::keep);
// (2)
template<typename IteratorType, typename SentinelType = IteratorType>
static basic_json from_bjdata(IteratorType first, SentinelType last,
                              const bool strict = true,
                              const bool allow_exceptions = true,
                              const error_handler_t error_handler = error_handler_t::keep);
```

Deserializes a given input to a JSON value using the BJData (Binary JData) 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](../../features/binary_formats/bjdata.md).

## 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 BJData 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 (`#!cpp true` by default)

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

`error_handler` (in)
:   how to treat a string value or object key that is not valid UTF-8; see [`error_handler_t`](error_handler_t.md).
    BJData does not require a decoder to reject ill-formed UTF-8, so checking is opt-in: the default, `keep`, does not
    check at all, as every binary reader did before this parameter was added; `strict` checks and throws;
    `replace`/`ignore` sanitize the string the same way [`dump`](dump.md) would

## Return value

deserialized JSON value; in case of a parse error and `allow_exceptions` set to `#!cpp false`, the return value will be
`value_t::discarded`. The latter can be checked with [`is_discarded`](is_discarded.md).

## Exception safety

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

## Exceptions

- Throws [parse_error.110](../../home/exceptions.md#jsonexceptionparse_error110) 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](../../home/exceptions.md#jsonexceptionparse_error112) if a parse error occurs
- Throws [parse_error.113](../../home/exceptions.md#jsonexceptionparse_error113) if a string could not be parsed
  successfully, or if a string value or object key is not valid UTF-8 and `error_handler` is `strict`
- Throws [parse_error.115](../../home/exceptions.md#jsonexceptionparse_error115) if the text of a high-precision
  number (`H`) is not a valid number
- Throws [out_of_range.408](../../home/exceptions.md#jsonexceptionout_of_range408) if the size of an optimized container
  cannot be represented by `std::size_t` or exceeds the container's `max_size()`, or if the product of the dimensions of
  an n-dimensional array overflows

## Complexity

Linear in the size of the input.

## Examples

??? example

    The example shows the deserialization of a byte vector in BJData format to a JSON value.
     
    ```cpp
    #include <iostream>
    #include <iomanip>
    #include <nlohmann/json.hpp>
    
    using 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 BJData
        json j = json::from_bjdata(v);
    
        // print the deserialized JSON value
        std::cout << std::setw(2) << j << '\n';
    }
    
    ```
    
    Output:
    
    ```json
    {
      "compact": true,
      "schema": 0
    }
    
    ```

## See also

- [BJData](../../features/binary_formats/bjdata.md) - the format, its byte layout and how values are mapped
- [Binary formats](../../features/binary_formats/index.md) - overview and comparison of the supported binary formats
- [Parsing untrusted input](../../features/parsing/untrusted_input.md) - limits and safe handling of hostile data
- [Binary values](../../features/binary_values.md) - how binary values and subtypes are handled
- [`to_bjdata`](to_bjdata.md) - create a BJData serialization of a JSON value
- [`from_cbor`](from_cbor.md) - create a JSON value from an input in CBOR format
- [`from_msgpack`](from_msgpack.md) - create a JSON value from an input in MessagePack format
- [`from_bson`](from_bson.md) - create a JSON value from an input in BSON format
- [`from_ubjson`](from_ubjson.md) - create a JSON value from an input in UBJSON format
- [`from_bon8`](from_bon8.md) - create a JSON value from an input in BON8 format

## Version history

- Added in version 3.11.0.
- 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.
- Added `error_handler` parameter in version 3.13.0.

!!! warning "Deprecation"

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

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