JSON for Modern C++ 3.8.0

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
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cbegin
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~basic_json
| ## ◆ operator[]() [8/8] template<typename T >
const_reference nlohmann::basic_json::operator[] | ( | T * | key | ) | const
| inline
  Returns a const reference to the element at with specified key key. No bounds checking is performed. Warning If the element with key key does not exist, the behavior is undefined. Parameters
  [in] | key | key of the element to access
  Returns const reference to the element at key key Precondition The element with key key must exist. This precondition is enforced with an assertion. Exceptions
  type_error.305 | if the JSON value is not an object; in that case, 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 using the `[]` operator. 1 #include <iostream> 2 #include <nlohmann/json.hpp> 3 4 using json = nlohmann::json; 5 6 int main() 7 { 8 // create a JSON object 9 const json object = 10 { 11 {"one", 1}, {"two", 2}, {"three", 2.9} 12 }; 13 14 // output element with key "two" 15 std::cout << object["two"] << '\n'; 16 } Output (play with this example online):
      2
  The example code above can be translated with
      g++ -std=c++11 -Isingle_include doc/examples/operatorarray__key_type_const.cpp -o operatorarray__key_type_const
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 20123 of file json.hpp.

nlohmann::json
basic_json<> json
default JSON class
Definition: json.hpp:2933