json/docs/mkdocs/docs/api/basic_json/from_bon8.md

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 (#!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.

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.
 
```cpp
--8<-- "examples/from_bon8.cpp"
```

Output:

```json
--8<-- "examples/from_bon8.output"
```

See also

• BON8 - the format, its byte layout and how values are mapped
• Binary formats - overview and comparison of the supported binary formats
• Parsing untrusted input - limits and safe handling of hostile data
• 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.

!!! 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.