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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.
The constructor has two parts. First is the initializer list which follows the parameter list and before the method body. It starts with a colon and entries are comma-separated. The initializer list is not required, but offers the opportunity to provide values for data members and avoid separate assignment statements.
A class in C++ is a user-defined type or data structure declared with any of the keywords class, struct or union (the first two are collectively referred to as non-union classes) that has data and functions (also called member variables and member functions) as its members whose access is governed by the three access specifiers private, protected or public.
The Standard C++ syntax for a non-placement new expression is [2] new new-type-id ( optional-initializer-expression-list) The placement syntax adds an expression list immediately after the new keyword. This expression list is the placement. It can contain any number of expressions. [2] [3] [6]
C++ also provides constructors to initialize an object, but they are often not as convenient as the initializer list. However, C++03 allows initializer-lists only on structs and classes that conform to the Plain Old Data (POD) definition; C++11 extends initializer-lists, so they can be used for all classes including standard containers like std ...
Copy constructors are the standard way of copying objects in C++, as opposed to cloning, and have C++-specific nuances. The first argument of such a constructor is a reference to an object of the same type as is being constructed (const or non-const), which might be followed by parameters of any type (all having default values).
[4] [5] Function types in C++ are usually hidden behind typedefs and typically have an explicit reference or pointer qualifier. To force the alternate interpretation, the typical technique is a different object creation or conversion syntax. In the type conversion example, there are two alternate syntaxes available for casts: the "C-style cast"