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

    #include <iostream>
    #include <iomanip>
    #include <nlohmann/json.hpp>

    using json = nlohmann::json;

    int main()
    {
        // create byte vector
        std::vector<std::uint8_t> v = {0xa2, 0x67, 0x63, 0x6f, 0x6d, 0x70, 0x61, 0x63,
                                       0x74, 0xf5, 0x66, 0x73, 0x63, 0x68, 0x65, 0x6d,
                                       0x61, 0x00
                                      };

        // deserialize it with CBOR
        json j = json::from_cbor(v);

        // print the deserialized JSON value
        std::cout << std::setw(2) << j << std::endl;
    }

Output:

    {
      "compact": true,
      "schema": 0
    }

## 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.

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 `from_cbor(ptr, len, ...);` with `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 `from_cbor({ptr, ptr+len}, ...);` with `from_cbor(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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