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nlohmann
118 lines
4.2 KiB
Markdown
118 lines
4.2 KiB
Markdown
# <small>nlohmann::basic_json::</small>from_msgpack
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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_msgpack(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>
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static basic_json from_msgpack(IteratorType first, IteratorType 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 MessagePack serialization format.
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1. Reads from a compatible input.
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2. Reads from an iterator range.
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The exact mapping and its limitations are described on a [dedicated page](../../features/binary_formats/messagepack.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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- an object `obj` for which `begin(obj)` and `end(obj)` produces a valid pair of iterators.
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`IteratorType`
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: a compatible iterator type
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## Parameters
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`i` (in)
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: an input in MessagePack 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
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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 unsupported features from
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MessagePack were used in the given input or if the input is not valid MessagePack
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- Throws [parse_error.113](../../home/exceptions.md#jsonexceptionparse_error113) if a string was expected as a map key,
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but not found
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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 MessagePack format to a JSON value.
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```cpp
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--8<-- "examples/from_msgpack.cpp"
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```
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Output:
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```json
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--8<-- "examples/from_msgpack.output"
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```
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## See also
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- [to_msgpack](to_msgpack.md) create a MessagePack 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_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 2.0.9.
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- Parameter `start_index` since version 2.1.1.
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- Changed to consume input adapters, removed `start_index` parameter, and added `strict` parameter in version 3.0.0.
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- Added `allow_exceptions` parameter in version 3.2.0.
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!!! warning "Deprecation"
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- Overload (2) replaces calls to `from_msgpack` with a pointer and a length as first two parameters, which has been
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deprecated in version 3.8.0. This overload will be removed in version 4.0.0. Please replace all calls like
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`#!cpp from_msgpack(ptr, len, ...);` with `#!cpp from_msgpack(ptr, ptr+len, ...);`.
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- Overload (2) replaces calls to `from_msgpack` with a pair of iterators as their first parameter, which has been
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deprecated in version 3.8.0. This overload will be removed in version 4.0.0. Please replace all calls like
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`#!cpp from_msgpack({ptr, ptr+len}, ...);` with `#!cpp from_msgpack(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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