In the C++ programming language, Object-Oriented Programming (OOP) is a good way to represent data and organize the functionality of your code into logical groups. Classes and Objects are the best way to work on properties and methods. One of the features of OOP IDE is copy assignment operator that is used with “operator=” to create a new object from an existing one. In this post, we explain the use of a forced default copy assignment operator with C++ examples.
Table of Contents
What are classes and objects in C++?
Classes are defined in C++ using 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, and they work as an object constructor. Objects are an instantiation of a class. In C++ programming, 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 Tmyclass { public: std::string str; }; |
then we can create our objects with this Type of myclass as below,
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Tmyclass o1, o2; |
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 forced (defaulted) copy assignment operator with default option;
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 |
What is a forced (default) copy assignment operator in C++?
The forced copy assignment operator forces a copy assignment operator to be generated by the compiler and it 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 to copy assignment operator with default option, here is a simple class
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class Tmyclass { public: std::string str; }; |
This is same as below.
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class Tmyclass { public: std::string str; Tmyclass& operator=( const Tmyclass& other) = default; // Forced (Default) Copy Assignment Operator }; |
As you see both are same, because this is default in any class declaration and it is automatically declared.
And here is how you can use this “=” copy assignment operator on the objects of one of these given class examples,
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Tmyclass o1, o2; o2 = o1; // Using Copy Assingment Operator |
Is there a full example to forced (default) copy assignment operator 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=( const Tmyclass& other) = default; // Forced (Default) Copy Assignment Operator }; 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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LearnCplusplus.org LearnCplusplus.org Press any key to continue . . . |
As you see, in Modern C++, we can simply use the default copy assignment operator in C++ without any declaration. We can specialize the “=” operator what to copy or not, with the copy assignment operator.
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