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nlohmann
98 lines
2.1 KiB
Markdown
98 lines
2.1 KiB
Markdown
# nlohmann::operator>>(basic_json)
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```
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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) : input stream to read a serialized JSON value from
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`j` (in, out) : 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`](https://json.nlohmann.me/home/exceptions/#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 [`parse_error.101`](https://json.nlohmann.me/home/exceptions/#jsonexceptionparse_error101) with a detailed message.
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Deprecation
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This function replaces function `std::istream& operator<<(basic_json& j, std::istream& i)` which has been deprecated in version 3.0.0. It will be removed in version 4.0.0. Please replace calls like `j << i;` with `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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```
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#include <iostream>
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#include <iomanip>
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#include <sstream>
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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 stream with serialized JSON
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std::stringstream ss;
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ss << R"({
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"number": 23,
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"string": "Hello, world!",
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"array": [1, 2, 3, 4, 5],
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"boolean": false,
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"null": null
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})";
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// create JSON value and read the serialization from the stream
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json j;
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ss >> j;
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// serialize JSON
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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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```
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{
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"array": [
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1,
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2,
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3,
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4,
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5
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],
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"boolean": false,
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"null": null,
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"number": 23,
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"string": "Hello, world!"
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}
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```
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## See also
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- [accept](https://json.nlohmann.me/api/basic_json/accept/index.md) - check if the input is valid JSON
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- [parse](https://json.nlohmann.me/api/basic_json/parse/index.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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