Object-Oriented Programming (OOP) is a method of mapping real-world objects and data to computer functions and data structures. Classes and Objects are part of object-oriented methods and typically provide features such as properties and methods. One of the features of an OOP tool is the copy assignment operator that is used with “operator=” to create a new object from an existing one. In this post, we explain the typical declaration of a copy assignment operator with C++ examples.
Table of Contents
What are classes and objects in C++?
Classes are defined in C++ using the keyword class followed by the name of the class. Classes are the blueprint for the objects and they are user-defined data types that we can use in our program. Objects are an instantiation of a class, In C++ programming, because it is designed to be strongly object oriented most of the commands are associated with classes and objects, along with their attributes and methods. Here is a simple class example below.
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class myclass { public: std::string str; }; |
What is a copy assignment operator in C++?
The Copy Assignment Operator in a class is a non-template non-static member function that is declared with the “operator=“. When you create a class or a type that is copy assignable (that you can copy with the = operator symbol), it must have a public copy assignment operator. Here is a simple syntax for the typical declaration of a copy assignment operator when the swap is used.
Syntax:
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class_name & class_name :: operator= ( class_name ) |
Here is an example in a class.
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class Tmyclass { public: Tmyclass& operator=(Tmyclass other) // Using Copy Assingment Operator { // Copy or swap things return *this; } }; |
What is a typical declaration of a copy assignment operator with std::swap?
Let’s give a simple C++ example of a typical declaration of a copy assignment operator with std::swap.
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class myclass { public: std::string str; myclass& operator=(myclass other) { std::cout << "Copy Assignment Operator is called \n"; std::swap(str, other.str); return *this; } }; |
And here is how you can use this “=” copy assignment operator:
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Tmyclass o1, o2; o2 = o1; // Using Copy Assingment Operator |
Is there a full example of a typical declaration of a copy assignment operator with std::swap in C++?
An example with a copy assignment operator in a class.
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#include <iostream> #include <string> class Tmyclass { public: std::string str; Tmyclass& operator=(Tmyclass other) // Using Copy Assignment Operator { std::cout << "Copy Assignment Operator is called" << std::endl; std::swap(str, other.str); return *this; } }; int main() { Tmyclass o1, o2; o1.str = "LearnCplusplus.org"; o2 = o1; // Using Copy Assingment Operator std::cout << o1.str << std::endl; std::cout << o2.str << std::endl; system("pause"); return 0; } |
Here is the output.
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Copy Assignment Operator is called LearnCplusplus.org LearnCplusplus.org Press any key to continue . . . |
As you see, in Modern C++, we can specialize the “=” operator what to copy or not, with the copy assignment operator.
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