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nlohmann
125 lines
4.5 KiB
Markdown
125 lines
4.5 KiB
Markdown
# nlohmann::basic_json::from_bson
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```
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// (1)
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template<typename InputType>
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static basic_json from_bson(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_bson(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 BSON (Binary JSON) serialization format.
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1. Reads from a compatible input.
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1. Reads from an iterator range.
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The exact mapping and its limitations are described on a [dedicated page](https://json.nlohmann.me/features/binary_formats/bson/index.md).
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## Template parameters
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`InputType` : A compatible input, for instance:
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```
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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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```
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`IteratorType` : a compatible iterator type
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## Parameters
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`i` (in) : an input in BSON format convertible to an input adapter
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`first` (in) : iterator to the start of the input
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`last` (in) : iterator to the end of the input
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`strict` (in) : whether to expect the input to be consumed until EOF (`true` by default)
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`allow_exceptions` (in) : whether to throw exceptions in case of a parse error (optional, `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 `false`, the return value will be `value_t::discarded`. The latter can be checked with [`is_discarded`](https://json.nlohmann.me/api/basic_json/is_discarded/index.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`](https://json.nlohmann.me/home/exceptions/#jsonexceptionparse_error110) if the given input ends prematurely or the end of the input was not reached when `strict` was set to true
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- Throws [`parse_error.112`](https://json.nlohmann.me/home/exceptions/#jsonexceptionparse_error112) if a parse error occurs (e.g., an invalid string or byte array length)
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- Throws [`parse_error.114`](https://json.nlohmann.me/home/exceptions/#jsonexceptionparse_error114) if an unsupported BSON record type is encountered
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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 BSON format to a JSON value.
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```
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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 = {0x1b, 0x00, 0x00, 0x00, 0x08, 0x63, 0x6f, 0x6d,
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0x70, 0x61, 0x63, 0x74, 0x00, 0x01, 0x10, 0x73,
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0x63, 0x68, 0x65, 0x6d, 0x61, 0x00, 0x00, 0x00,
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0x00, 0x00, 0x00
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};
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// deserialize it with BSON
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json j = json::from_bson(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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```
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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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- [BSON specification](http://bsonspec.org/spec.html)
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- [to_bson](https://json.nlohmann.me/api/basic_json/to_bson/index.md) for the analogous serialization
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- [from_cbor](https://json.nlohmann.me/api/basic_json/from_cbor/index.md) for the related CBOR format
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- [from_msgpack](https://json.nlohmann.me/api/basic_json/from_msgpack/index.md) for the related MessagePack format
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- [from_ubjson](https://json.nlohmann.me/api/basic_json/from_ubjson/index.md) for the related UBJSON format
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- [from_bjdata](https://json.nlohmann.me/api/basic_json/from_bjdata/index.md) for the related BJData format
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## Version history
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- Added in version 3.4.0.
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Deprecation
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- Overload (2) replaces calls to `from_bson` 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_bson(ptr, len, ...);` with `from_bson(ptr, ptr+len, ...);`.
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- Overload (2) replaces calls to `from_bson` 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_bson({ptr, ptr+len}, ...);` with `from_bson(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 function.
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