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A map, sometimes referred to as a dictionary, consists of a key/value pair. The key is used to order the sequence, and the value is somehow associated with that key. For example, a map might contain keys representing every unique word in a text and values representing the number of times that word appears in the text.
In C++, a constructor of a class/struct can have an initializer list within the definition but prior to the constructor body. It is important to note that when you use an initialization list, the values are not assigned to the variable. They are initialized. In the below example, 0 is initialized into re and im. Example:
<initializer_list> Added in C++11. Provides initializer list support. <limits> Provides the class template std::numeric_limits, used for describing properties of fundamental numeric types. <new> Provides operators new and delete and other functions and types composing the fundamentals of C++ memory management. <source_location> Added in C++20.
Initialization of STL containers with constants within the source code is not as easy as data structures inherited from C (addressed in C++11 with initializer lists). STL containers are not intended to be used as base classes (their destructors are deliberately non-virtual); deriving from a container is a common mistake. [9] [10]
In object-oriented programming, the iterator pattern is a design pattern in which an iterator is used to traverse a container and access the container's elements. The iterator pattern decouples algorithms from containers; in some cases, algorithms are necessarily container-specific and thus cannot be decoupled.
The template class std::initializer_list<> is a first-class C++11 standard library type. They can be constructed statically by the C++11 compiler via use of the {} syntax without a type name in contexts where such braces will deduce to an std::initializer_list , or by explicitly specifying the type like std::initializer_list<SomeType>{args ...
The implicit copy constructor of a class calls base copy constructors and copies its members by means appropriate to their type. If it is a class type, the copy constructor is called. If it is a scalar type, the built-in assignment operator is used. Finally, if it is an array, each element is copied in the manner appropriate to its type. [3]
When a class constructor does not explicitly call the constructor of one of its object-valued fields in its initializer list, the default constructor for the field's class is called. In the standard library, certain containers "fill in" values using the default constructor when the value is not given explicitly.