JSON for Modern C++ 2.1.1
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◆ operator[]() [7/10]

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>
template<typename T , std::size_t n>
reference nlohmann::basic_json< ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer >::operator[] ( T *(&)  key[n])
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\n Logarithmic in the size of the container.
Example\n The example below shows how object elements can be read and
written using the [] operator.
1#include <json.hpp>
2
3using json = nlohmann::json;
4
5int 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}
static basic_json array(std::initializer_list< basic_json > init=std::initializer_list< basic_json >())
explicitly create an array from an initializer list
Definition json.hpp:2165
a class to store JSON values
Definition json.hpp:1040
basic_json<> json
default JSON class
Definition json.hpp:12369

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 3887 of file json.hpp.