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¶

• Throws parse_error.101 in case of an unexpected token.

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.

Invalid Unicode escapes and unpaired surrogates in the input are reported as parse_error.101 with a detailed message.

operator>> parses exactly one JSON value and leaves the stream positioned right after it, so it can be called repeatedly to read a sequence of concatenated JSON values from the same stream:

jsonj1,j2;
input>>j1;// parses the first value, stream now positioned right after it
input>>j2;// parses the next value

Note this does not work for JSON Lines (newline-delimited JSON) input -- see that page for why and for the recommended alternative.

Examples¶

#include<iostream>
#include<iomanip>
#include<sstream>
#include<nlohmann/json.hpp>
usingjson=nlohmann::json;
intmain()
{
// create stream with serialized JSON
std::stringstreamss;
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
jsonj;
ss>>j;
// serialize JSON
std::cout<<std::setw(2)<<j<<'\n';
}

{
"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.