One of the most commonly used features of C++ software, in common with many programming languages, are assignment operators. These take the form of copy assignment and move assignment operators. In C++, a copy assignment operator can be used with “operator=” to create a new object from an existing one. In this post, we explain assignment operators with copy assignment operator examples in C++.
If you are looking for more information on assignment operators in C or C++, the following post discusses them in depth.
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 which is defaulted,
Syntax (Since C++11).
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class_name & class_name :: operator= ( const class_name& ) = default; |
Here is an example in a class.
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Tmyclass& operator=(const Tmyclass& other) = default; // Copy Assignment Operator |
Is there a simple example of using the assignment operator in C++?
The forced copy assignment operator is default in any class declarations. This means you don’t need to declare it as above. Let’s give examples without using it.
Let’s give a simple C++ example of a copy assignment operator with default option. Here is a simple class:
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class myclass { public: std::string str; }; |
Because this is default in any class declaration, and it is automatically declared. This class is same as below.
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class myclass { public: std::string str; Tmyclass& operator=(const Tmyclass& other) = default; // Copy Assignment Operator }; |
And here is how you can use this “=” copy assignment operator with both class examples above.
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Tmyclass o1, o2; o2 = o1; // Copy Assingment Operator |
Is there a full example of how to use the assignment operator in C++?
Here is 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=(const Tmyclass& other) = default; // Copy Assignment Operator }; int main() { Tmyclass o1, o2; o1.str = "LearnCplusplus.org"; o2 = o1; // Using Copy Assignment 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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LearnCplusplus.org LearnCplusplus.org Press any key to continue . . . |
As you see, in Modern C++, we can specialize the “=” operator on what to copy or not, with the copy assignment operator.
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