174 lines
7.6 KiB
Markdown
174 lines
7.6 KiB
Markdown
# <small>nlohmann::basic_json::</small>from_ubjson
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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_ubjson(InputType&& i,
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const bool strict = true,
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const bool allow_exceptions = true,
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const error_handler_t error_handler = error_handler_t::keep);
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// (2)
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template<typename IteratorType, typename SentinelType = IteratorType>
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static basic_json from_ubjson(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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const error_handler_t error_handler = error_handler_t::keep);
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```
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Deserializes a given input to a JSON value using the UBJSON (Universal Binary JSON) 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/ubjson.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 UBJSON 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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`error_handler` (in)
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: how to treat a string value or object key that is not valid UTF-8; see [`error_handler_t`](error_handler_t.md).
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UBJSON does not require a decoder to reject ill-formed UTF-8, so checking is opt-in: the default, `keep`, does not
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check at all, as every binary reader did before this parameter was added; `strict` checks and throws;
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`replace`/`ignore` sanitize the string the same way [`dump`](dump.md) would
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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 an invalid type marker is read
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(including a type marker after `$` of an optimized container, even if its count is 0), or if `$` is not followed by `#`
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- Throws [parse_error.113](../../home/exceptions.md#jsonexceptionparse_error113) if a string could not be parsed
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successfully (negative or non-integer length, `C` followed by a byte above 0x7F), if the count of an optimized
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container is negative, or if a string value or object key is not valid UTF-8 and `error_handler` is `strict`
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- Throws [parse_error.115](../../home/exceptions.md#jsonexceptionparse_error115) if the text of a high-precision number
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(`H`) is not a valid JSON number
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- Throws [out_of_range.406](../../home/exceptions.md#jsonexceptionout_of_range406) if a high-precision number, or a
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float64 when `number_float_t` is `float`, does not fit into `number_float_t`
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- Throws [out_of_range.408](../../home/exceptions.md#jsonexceptionout_of_range408) if the count of an optimized
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container exceeds the capacity of the container (or of `std::size_t`), or if an optimized array of `Z`, `T`, or `F` has
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more than 1,048,576 elements
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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 UBJSON 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 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 = {0x7B, 0x69, 0x07, 0x63, 0x6F, 0x6D, 0x70, 0x61,
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0x63, 0x74, 0x54, 0x69, 0x06, 0x73, 0x63, 0x68,
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0x65, 0x6D, 0x61, 0x69, 0x00, 0x7D
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};
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// deserialize it with UBJSON
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json j = json::from_ubjson(v);
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// print the deserialized JSON value
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std::cout << std::setw(2) << j << '\n';
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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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"schema": 0
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}
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```
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## See also
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- [UBJSON](../../features/binary_formats/ubjson.md) - the format, its byte layout and how values are mapped
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- [Binary formats](../../features/binary_formats/index.md) - overview and comparison of the supported binary formats
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- [Parsing untrusted input](../../features/parsing/untrusted_input.md) - limits and safe handling of hostile data
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- [Binary values](../../features/binary_values.md) - how binary values and subtypes are handled
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- [`to_ubjson`](to_ubjson.md) - create a UBJSON 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_bjdata`](from_bjdata.md) - create a JSON value from an input in BJData format
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- [`from_bon8`](from_bon8.md) - create a JSON value from an input in BON8 format
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## Version history
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- Added in version 3.1.0.
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- Added `allow_exceptions` parameter in version 3.2.0.
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- Extended container support (1) to include types with lvalue-only ADL `begin`/`end` (matching `std::begin`/`std::end` semantics) in version 3.13.0.
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- Extended overload (2) to accept heterogeneous iterator+sentinel pairs (C++20 ranges support) in version 3.13.0.
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- Added `error_handler` parameter in version 3.13.0.
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!!! warning "Deprecation"
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- Overload (2) replaces calls to `from_ubjson` with a pointer and a length as first two parameters, which has been
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deprecated in version 3.8.0. 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_ubjson(ptr, len, ...);` with `#!cpp from_ubjson(ptr, ptr+len, ...);`.
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- Overload (2) replaces calls to `from_ubjson` 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_ubjson({ptr, ptr+len}, ...);` with `#!cpp from_ubjson(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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See the [migration guide](../../integration/migration_guide.md#parsing) for how to update existing code.
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