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145 lines
4.8 KiB
Markdown
145 lines
4.8 KiB
Markdown
# <small>nlohmann::basic_json::</small>from_bon8
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```cpp
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// (1)
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template<typename InputType>
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static basic_json from_bon8(InputType&& i,
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const bool strict = true,
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const bool allow_exceptions = true);
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// (2)
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template<typename IteratorType, typename SentinelType = IteratorType>
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static basic_json from_bon8(IteratorType first, SentinelType last,
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const bool strict = true,
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const bool allow_exceptions = true);
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```
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Deserializes a given input to a JSON value using the BON8 (Binary Object Notation 8) serialization format.
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1. Reads from a compatible input.
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2. Reads from an iterator range, or an iterator and a sentinel of a different type (C++20 ranges support).
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The exact mapping and its limitations are described on a [dedicated page](../../features/binary_formats/bon8.md).
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## Template parameters
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`InputType`
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: A compatible input, for instance:
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- an `std::istream` object
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- a `FILE` pointer
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- a C-style array of characters
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- a pointer to a null-terminated string of single byte characters
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- a container `obj` for which `begin(obj)` and `end(obj)` produce a valid pair of iterators
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(as found via ADL or member functions, with semantics compatible to `std::begin` and `std::end`)
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`IteratorType`
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: a compatible iterator type
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`SentinelType`
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: defaults to `IteratorType`; may be a different type comparable to `IteratorType` via `operator!=`, for instance.
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- a custom sentinel type for C++20 ranges
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- `std::default_sentinel_t`, when `IteratorType` is `std::counted_iterator`
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## Parameters
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`i` (in)
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: an input in BON8 format convertible to an input adapter
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`first` (in)
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: iterator to the start of the input
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`last` (in)
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: iterator to the end of the input, or a sentinel value that compares equal to the end iterator with `operator!=`
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`strict` (in)
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: whether to expect the input to be consumed until EOF (`#!cpp true` by default)
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`allow_exceptions` (in)
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: whether to throw exceptions in case of a parse error (optional, `#!cpp true` by default)
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## Return value
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deserialized JSON value; in case of a parse error and `allow_exceptions` set to `#!cpp false`, the return value will be
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`value_t::discarded`. The latter can be checked with [`is_discarded`](is_discarded.md).
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## Exception safety
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Strong guarantee: if an exception is thrown, there are no changes in the JSON value.
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## Exceptions
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- Throws [parse_error.110](../../home/exceptions.md#jsonexceptionparse_error110) if the given input ends prematurely or
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the end of the file was not reached when `strict` was set to true
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- Throws [parse_error.112](../../home/exceptions.md#jsonexceptionparse_error112) if a parse error occurs, for instance
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an invalid byte, a string that is not valid UTF-8, or an object key that is not a string
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## Complexity
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Linear in the size of the input.
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## Examples
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??? example
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The example shows the deserialization of a byte vector in BON8 format to a JSON value.
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```cpp
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#include <iostream>
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#include <iomanip>
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#include <nlohmann/json.hpp>
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using json = nlohmann::json;
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int main()
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{
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// create byte vector
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std::vector<std::uint8_t> v = {0x89, 0x63, 0x6f, 0x6d, 0x70, 0x61, 0x63, 0x74,
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0xf9, 0x66, 0x6f, 0x72, 0x6d, 0x61, 0x74, 0xff,
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0x42, 0x4f, 0x4e, 0x38, 0xff, 0x73, 0x63, 0x68,
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0x65, 0x6d, 0x61, 0x90
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};
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// deserialize it with BON8
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json j = json::from_bon8(v);
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// print the deserialized JSON value
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std::cout << std::setw(2) << j << std::endl;
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}
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```
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Output:
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```json
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{
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"compact": true,
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"format": "BON8",
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"schema": 0
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}
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```
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## See also
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- [to_bon8](to_bon8.md) create a BON8 serialization of a JSON value
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- [from_cbor](from_cbor.md) create a JSON value from an input in CBOR format
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- [from_msgpack](from_msgpack.md) create a JSON value from an input in MessagePack format
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- [from_bson](from_bson.md) create a JSON value from an input in BSON format
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- [from_ubjson](from_ubjson.md) create a JSON value from an input in UBJSON format
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- [from_bjdata](from_bjdata.md) create a JSON value from an input in BJData format
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## Version history
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- Added in version 3.13.0.
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!!! warning "Deprecation"
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- Overload (2) replaces calls to `from_bon8` with a pointer and a length as first two parameters, which has been
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deprecated in version 3.13.0. In version 4.0.0, this overload
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will be deleted (`= delete`) rather than removed. Please replace all calls like
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`#!cpp from_bon8(ptr, len, ...);` with `#!cpp from_bon8(ptr, ptr+len, ...);`.
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You should be warned by your compiler with a `-Wdeprecated-declarations` warning if you are using a deprecated
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function.
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