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101 lines
3.5 KiB
Markdown
101 lines
3.5 KiB
Markdown
# <small>nlohmann::basic_json::</small>to_bson
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```cpp
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// (1)
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static std::vector<std::uint8_t> to_bson(const basic_json& j);
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// (2)
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static void to_bson(const basic_json& j, detail::output_adapter<std::uint8_t> o);
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static void to_bson(const basic_json& j, detail::output_adapter<char> o);
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```
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BSON (Binary JSON) is a binary format in which zero or more ordered key/value pairs are stored as a single entity (a
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so-called document).
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1. Returns a byte vector containing the BSON serialization.
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2. Writes the BSON serialization to an output adapter.
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The exact mapping and its limitations are described on a [dedicated page](../../features/binary_formats/bson.md).
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## Parameters
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`j` (in)
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: JSON value to serialize
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`o` (in)
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: output adapter to write serialization to
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## Return value
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1. BSON serialization as a byte vector
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2. (none)
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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 [`type_error.317`](../../home/exceptions.md#jsonexceptiontype_error317) if the top-level type of the JSON value
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is not an object; example: `"to serialize to BSON, top-level type must be object, but is string"`
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- Throws [`out_of_range.409`](../../home/exceptions.md#jsonexceptionout_of_range409) if a key in the JSON object contains
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a null byte (code point U+0000); example: `"BSON key cannot contain code point U+0000 (at byte 2)"`
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- Throws [`out_of_range.412`](../../home/exceptions.md#jsonexceptionout_of_range412) if the length of a document, array,
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string, or binary value exceeds the range of the 32-bit BSON length field; example:
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`"BSON length 2147483661 exceeds maximum of 2147483647"`
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- Throws [`out_of_range.415`](../../home/exceptions.md#jsonexceptionout_of_range415) if the subtype of a binary value
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exceeds 255, the maximum of the BSON binary subtype; example:
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`"subtype 70000 is too large for the BSON binary subtype (max 255)"`
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## Complexity
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Linear in the size of the JSON value `j`. The length prefixes of all nested documents and arrays are computed in one
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pass before anything is written.
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## Examples
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??? example "Example: serialize a JSON value to BSON"
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The example shows the serialization of a JSON value to a byte vector in BSON format.
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```cpp
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--8<-- "examples/to_bson.cpp"
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```
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Output:
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```json
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--8<-- "examples/to_bson.output"
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```
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??? example "Example: out_of_range.409 exception"
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The example shows how serializing a JSON object whose key contains a null byte (U+0000) throws an exception, because
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BSON keys are null-terminated C strings and cannot contain U+0000 themselves.
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```cpp
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--8<-- "examples/to_bson__exception.cpp"
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```
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Output:
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```json
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--8<-- "examples/to_bson__exception.output"
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```
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## See also
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- [from_bson](from_bson.md) create a JSON value from an input in BSON format
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- [to_cbor](to_cbor.md) create a CBOR serialization of a JSON value
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- [to_msgpack](to_msgpack.md) create a MessagePack serialization of a JSON value
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- [to_ubjson](to_ubjson.md) create a UBJSON serialization of a JSON value
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- [to_bjdata](to_bjdata.md) create a BJData serialization of a JSON value
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- [to_bon8](to_bon8.md) create a BON8 serialization of a JSON value
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## Version history
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- Added in version 3.4.0.
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- Throws `out_of_range.412` and `out_of_range.415` since version 3.13.0.
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- Linear in the size of `j`, and no longer limited by the call stack for deeply nested values, since version 3.13.0.
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- `out_of_range.415` is now detected before anything is written, like the other exceptions above, since version 3.13.0.
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