api/basic_json/from_bon8.md

# <small>nlohmann::basic_json::</small>from_bon8

```cpp
// (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](../../features/binary_formats/bon8.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 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 (`#!cpp true` by default)

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

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

## 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.
     
    ```cpp
    #include <iostream>
    #include <iomanip>
    #include <nlohmann/json.hpp>
    
    using json = 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 << std::endl;
    }
    
    ```
    
    Output:
    
    ```json
    {
      "compact": true,
      "format": "BON8",
      "schema": 0
    }
    
    ```

## See also

- [to_bon8](to_bon8.md) create a BON8 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_bjdata](from_bjdata.md) create a JSON value from an input in BJData format

## Version history

- Added in version 3.13.0.

!!! warning "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. In version 4.0.0, this overload
      will be deleted (`= delete`) rather than removed. Please replace all calls like
      `#!cpp from_bon8(ptr, len, ...);` with `#!cpp from_bon8(ptr, ptr+len, ...);`.

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