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nlohmann
78 lines
2.0 KiB
Markdown
78 lines
2.0 KiB
Markdown
# <small>nlohmann::</small>operator>>(basic_json)
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```cpp
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std::istream& operator>>(std::istream& i, basic_json& j);
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```
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Deserializes an input stream to a JSON value.
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## Parameters
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`i` (in, out)
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: input stream to read a serialized JSON value from
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`j` (in, out)
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: JSON value to write the deserialized input to
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## Return value
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the stream `i`
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## Exceptions
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- Throws [`parse_error.101`](../home/exceptions.md#jsonexceptionparse_error101) in case of an unexpected token.
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## Complexity
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Linear in the length of the input. The parser is a predictive LL(1) parser.
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## Notes
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A UTF-8 byte order mark is silently ignored.
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Invalid Unicode escapes and unpaired surrogates in the input are reported as
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[`parse_error.101`](../home/exceptions.md#jsonexceptionparse_error101) with a detailed message.
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`operator>>` parses exactly one JSON value and leaves the stream positioned right after it, so it can be called
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repeatedly to read a sequence of concatenated JSON values from the same stream:
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```cpp
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json j1, j2;
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input >> j1; // parses the first value, stream now positioned right after it
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input >> j2; // parses the next value
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```
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Note this does **not** work for [JSON Lines](../features/parsing/json_lines.md) (newline-delimited JSON) input --
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see that page for why and for the recommended alternative.
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!!! warning "Deprecation"
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This function replaces function `#!cpp std::istream& operator<<(basic_json& j, std::istream& i)` which has
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been deprecated in version 3.0.0. It will be removed in version 4.0.0. Please replace calls like `#!cpp j << i;`
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with `#!cpp i >> j;`.
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## Examples
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??? example
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The example below shows how a JSON value is constructed by reading a serialization from a stream.
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```cpp
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--8<-- "examples/operator_deserialize.cpp"
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```
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Output:
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```json
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--8<-- "examples/operator_deserialize.output"
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```
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## See also
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- [accept](basic_json/accept.md) - check if the input is valid JSON
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- [parse](basic_json/parse.md) - deserialize from a compatible input
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## Version history
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- Added in version 1.0.0.
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