JSON for Modern C++ 3.7.3

accept
accept
accept
allocator_type
array
array_t
at
at
at
at
at
at
back
back
basic_json
basic_json
basic_json
basic_json
basic_json
basic_json
basic_json
basic_json
basic_json
basic_json
begin
begin
binary
binary
binary
binary
binary_t
boolean_t
cbegin
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empty
end
end
erase
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front
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operator<<
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operator[]
operator[]
operator[]
operator[]
operator[]
operator[]
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value_type
~basic_json
| ## ◆ operator[]() [7/8] template<typename T >
reference nlohmann::basic_json::operator[] | ( | T * | 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] | key | key of the element to access
  Returns reference to the element at key key Exceptions
  type_error.305 | if the JSON value is not an object or null; in that cases, using the [] operator with a key makes no sense.
  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 <iostream> 2 #include <iomanip> 3 #include <nlohmann/json.hpp> 4 5 using json = nlohmann::json; 6 7 int main() 8 { 9 // create a JSON object 10 json object = 11 { 12 {"one", 1}, {"two", 2}, {"three", 2.9} 13 }; 14 15 // output element with key "two" 16 std::cout << object["two"] << "\n\n"; 17 18 // change element with key "three" 19 object["three"] = 3; 20 21 // output changed array 22 std::cout << std::setw(4) << object << "\n\n"; 23 24 // mention nonexisting key 25 object["four"]; 26 27 // write to nonexisting key 28 object["five"]["really"]["nested"] = true; 29 30 // output changed object 31 std::cout << std::setw(4) << object << '\n'; 32 } 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 -Isingle_include 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 1.1.0 Definition at line 19459 of file json.hpp.

nlohmann::json
basic_json<> json
default JSON class
Definition: json.hpp:2774