JSON for Modern C++  3.7.2

◆ operator>> [2/2]

template<template< typename U, typename V, typename... Args > class ObjectType = std::map, template< typename U, typename... Args > class ArrayType = std::vector, class StringType = std::string, class BooleanType = bool, class NumberIntegerType = std::int64_t, class NumberUnsignedType = std::uint64_t, class NumberFloatType = double, template< typename U > class AllocatorType = std::allocator, template< typename T, typename SFINAE=void > class JSONSerializer = adl_serializer>
std::istream& operator>> ( std::istream &  i,
basic_json j 
)
friend

Deserializes an input stream to a JSON value.

Parameters
[in,out]iinput stream to read a serialized JSON value from
[in,out]jJSON value to write the deserialized input to
Exceptions
parse_error.101in case of an unexpected token
parse_error.102if to_unicode fails or surrogate error
parse_error.103if to_unicode fails
Complexity
Linear in the length of the input. The parser is a predictive LL(1) parser.
Note
A UTF-8 byte order mark is silently ignored.
Example
The example below shows how a JSON value is constructed by reading a serialization from a stream.
1 #include <iostream>
2 #include <iomanip>
3 #include <sstream>
4 #include <nlohmann/json.hpp>
5 
6 using json = nlohmann::json;
7 
8 int main()
9 {
10  // create stream with serialized JSON
11  std::stringstream ss;
12  ss << R"({
13  "number": 23,
14  "string": "Hello, world!",
15  "array": [1, 2, 3, 4, 5],
16  "boolean": false,
17  "null": null
18  })";
19 
20  // create JSON value and read the serialization from the stream
21  json j;
22  ss >> j;
23 
24  // serialize JSON
25  std::cout << std::setw(2) << j << '\n';
26 }

Output (play with this example online):
{
  "array": [
    1,
    2,
    3,
    4,
    5
  ],
  "boolean": false,
  "null": null,
  "number": 23,
  "string": "Hello, world!"
}
The example code above can be translated with
g++ -std=c++11 -Isingle_include doc/examples/operator_deserialize.cpp -o operator_deserialize 
See also
parse(std::istream&, const parser_callback_t) for a variant with a parser callback function to filter values while parsing
Since
version 1.0.0

Definition at line 20956 of file json.hpp.

nlohmann::json
basic_json<> json
default JSON class
Definition: json.hpp:2445