![]() It also lets you copy from const objects. This prevents the copy constructor from accidentally changing the copied object. ![]() Make the type of the copy constructor's argument const ClassName& whenever possible. Window& operator=(const Window& x) // Declare copy assignment. Window( const Window& ) // Declare copy constructor. For example: // spec1_copying_class_objects.cpp The copy constructor takes an argument of type ClassName&, where ClassName is the name of the class. When you implement both, the meaning of the code is clear. If you implement either one, we recommend that you implement the other one, too. Declaring a copy constructor doesn't suppress the compiler-generated copy assignment operator, and vice-versa. Similarly, if you don't declare a copy assignment operator, the compiler generates a member-wise copy assignment operator for you. If you don't declare a copy constructor, the compiler generates a member-wise copy constructor for you. Use an assignment operator operator= that returns a reference to the class type and takes one parameter that's passed by const reference-for example ClassName& operator=(const ClassName& x). The preceding code could mean "copy the contents of FILE1.DAT to FILE2.DAT" or it could mean "ignore FILE2.DAT and make b a second handle to FILE1.DAT." You must attach appropriate copying semantics to each class, as follows: ![]() For example, consider this code: TextFile a, b You can define the semantics of "copy" for objects of class type. Initialization: Initialization occurs when you declare a new object, when you pass function arguments by value, or when you return by value from a function. So, this code copies the value of b into a: Point a, b For information about move assignment, see Move Constructors and Move Assignment Operators (C++).īoth the assignment operation and the initialization operation cause objects to be copied.Īssignment: When one object's value is assigned to another object, the first object is copied to the second object. In this article "assignment" means copy assignment unless explicitly stated otherwise. Starting in C++11, two kinds of assignment are supported in the language: copy assignment and move assignment.
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