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nlohmann::operator>>(basic_json)

std::istream& operator>>(std::istream& i, basic_json& j);

Deserializes an input stream to a JSON value.

Parameters

i (in, out)
input stream to read a serialized JSON value from
j (in, out)
JSON value to write the deserialized input to

Return value

the stream i

Exceptions

Complexity

Linear in the length of the input. The parser is a predictive LL(1) parser.

Notes

A UTF-8 byte order mark is silently ignored.

Deprecation

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;.

Examples

Example

The example below shows how a JSON value is constructed by reading a serialization from a stream.

#include <iostream>
#include <iomanip>
#include <sstream>
#include <nlohmann/json.hpp>

using json = nlohmann::json;

int main()
{
    // create stream with serialized JSON
    std::stringstream ss;
    ss << R"({
        "number": 23,
        "string": "Hello, world!",
        "array": [1, 2, 3, 4, 5],
        "boolean": false,
        "null": null
    })";

    // create JSON value and read the serialization from the stream
    json j;
    ss >> j;

    // serialize JSON
    std::cout << std::setw(2) << j << '\n';
}

Output:

{
  "array": [
    1,
    2,
    3,
    4,
    5
  ],
  "boolean": false,
  "null": null,
  "number": 23,
  "string": "Hello, world!"
}

See also

  • accept - check if the input is valid JSON
  • parse - deserialize from a compatible input

Version history

  • Added in version 1.0.0. Deprecated in version 3.0.0.

Last update: August 12, 2022