JSON for Modern C++  2.0.0
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 = int64_t, class NumberUnsignedType = uint64_t, class NumberFloatType = double, template< typename U > class AllocatorType = std::allocator>
reference nlohmann::basic_json::operator[] ( const typename object_t::key_type &  key)
inline

Returns a reference to the element at with specified key key.

Note
If key is not found in the object, then it is silently added to the object and filled with a null value to make key a valid reference. In case the value was null before, it is converted to an object.
Parameters
[in]keykey of the element to access
Returns
reference to the element at key key
Exceptions
std::domain_errorif JSON is not an object or null; example: "cannot use operator[] with string"
Complexity
Logarithmic in the size of the container.
Example
The example below shows how object elements can be read and written using the [] operator.
1 #include <json.hpp>
2 
3 using json = nlohmann::json;
4 
5 int main()
6 {
7  // create a JSON object
8  json object =
9  {
10  {"one", 1}, {"two", 2}, {"three", 2.9}
11  };
12 
13  // output element with key "two"
14  std::cout << object["two"] << "\n\n";
15 
16  // change element with key "three"
17  object["three"] = 3;
18 
19  // output changed array
20  std::cout << std::setw(4) << object << "\n\n";
21 
22  // mention nonexisting key
23  object["four"];
24 
25  // write to nonexisting key
26  object["five"]["really"]["nested"] = true;
27 
28  // output changed object
29  std::cout << std::setw(4) << object << '\n';
30 }
basic_json<> json
default JSON class
Definition: json.hpp:8653
Output (play with this example online):
2

{
    "one": 1,
    "three": 3,
    "two": 2
}

{
    "five": {
        "really": {
            "nested": true
        }
    },
    "four": null,
    "one": 1,
    "three": 3,
    "two": 2
}
The example code above can be translated with
g++ -std=c++11 -Isrc doc/examples/operatorarray__key_type.cpp -o operatorarray__key_type 
See also
at(const typename object_t::key_type&) for access by reference with range checking
value() for access by value with a default value
Since
version 1.0.0

Definition at line 3275 of file json.hpp.