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◆ operator[]() [8/10]
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>
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.
- Note
- This function is required for compatibility reasons with Clang.
- Parameters
-
[in] | key | key of the element to access |
- Returns
- const reference to the element at key key
- Exceptions
-
std::domain_error | if JSON is not an object; example: "cannot use
operator[] with null" |
- Complexity\n Logarithmic in the size of the container.
- Example\n The example below shows how object elements can be read using
- the
[] operator.
10 { "one", 1}, { "two", 2}, { "three", 2.9}
14 std::cout << object[ "two"] << '\n';
static basic_json array(std::initializer_list< basic_json > init=std::initializer_list< basic_json >()) explicitly create an array from an initializer list
a class to store JSON values
basic_json<> json default JSON class
Output (play with this example online):
2
The example code above can be translated with g++ -std=c++11 -Isrc 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 1.0.0
Definition at line 3922 of file json.hpp.
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