json/doc/mkdocs/docs/api/basic_json/from_cbor.md

nlohmann::basic_json::from_cbor

// (1)
template<typename InputType>
static basic_json from_cbor(InputType&& i,
                            const bool strict = true,
                            const bool allow_exceptions = true,
                            const cbor_tag_handler_t tag_handler = cbor_tag_handler_t::error);

// (2)
template<typename IteratorType>
static basic_json from_cbor(IteratorType first, IteratorType last,
                            const bool strict = true,
                            const bool allow_exceptions = true,
                            const cbor_tag_handler_t tag_handler = cbor_tag_handler_t::error);

Deserializes a given input to a JSON value using the CBOR (Concise Binary Object Representation) 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 CBOR 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 (#!cpp true by default)

allow_exceptions (in)

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

tag_handler (in)

how to treat CBOR tags (optional, error by default); see cbor_tag_handler_t for more information

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 file was not reached when strict was set to true
• Throws parse_error.112 if unsupported features from CBOR were used in the given input or if the input is not valid CBOR
• Throws parse_error.113 if a string was expected as map key, but not found

Complexity

Linear in the size of the input.

Examples

??? example

The example shows the deserialization of a byte vector in CBOR format to a JSON value.
 
```cpp
--8<-- "examples/from_cbor.cpp"
```

Output:

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

Version history

• Added in version 2.0.9.
• Parameter start_index since version 2.1.1.
• Changed to consume input adapters, removed start_index parameter, and added strict parameter in version 3.0.0.
• Added allow_exceptions parameter in version 3.2.0.
• Added tag_handler parameter in version 3.9.0.

!!! warning "Deprecation"

- Overload (2) replaces calls to `from_cbor` 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
  `#!cpp from_cbor(ptr, len, ...);` with `#!cpp from_cbor(ptr, ptr+len, ...);`.
- Overload (2) replaces calls to `from_cbor` 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
  `#!cpp from_cbor({ptr, ptr+len}, ...);` with `#!cpp from_cbor(ptr, ptr+len, ...);`.

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