Do you want to learn what is Eligible Copy Constructor or what kind of methods are available to declare and use an Eligible Copy Constructor? In this post, we will try to explain the Eligible Copy Constructor with examples. First, let’s remind ourselves of the Constructor and Copy Constructor meaning in C+++ software.
What is a Constructor in C++ software?
The Constructor in C++ is a function, a method in the class, but it is a ‘special method’ that is automatically called when an object of a class is created. We don’t need to call this function. Whenever a new object of a class is created, the Constructor allows the class to initialize member variables or allocate storage. This is why the name Constructor is given to this special method. Here is a simple constructor class example below,
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class myclass { public: myclass() { std::cout << "myclass is constructed!\n"; }; }; |
There are different constructor types in classes and the Copy Constructor is one of these. Copy Constructors not only used in classes but also used with struct and union data types
The Copy Constructor in classes (class_name) is a non-template constructor whose first parameter is class_name&, const class_name&, volatile class_name&, or const volatile class_name& . It can be used with no other parameters or with the rest of the parameters all have default values.
The Copy Constructor is a constructor type for classes that class_name must name the current class, or it should be a qualified class name when it is declared at namespace scope or in a friend declaration.
What is a C++ Eligible Copy Constructor?
Since C++11, a copy constructor is defined as eligible if it is not deleted.
Since C++20, a copy constructor is eligible if
- Copy Constructor is not deleted, and
- Copy Constructor associated constraints, if any, are satisfied,
- no copy constructor with the same first parameter type is more constrained than it
The triviality of eligible copy constructors determines whether the class is an implicit-lifetime type and whether the class is a trivially copyable type.
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class myclass { public: myclass(const myclass&) // Eligible Copy Constructor { }; }; |
Here is a full C++ example of using an Eligible Copy Constuctor
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#include <iostream> class myclass { public: int param = 0; myclass() // Default Constructor { }; myclass(const myclass& a) // Eligible Copy Constructor { param =a.param; }; }; class my_otherclass : public myclass { // This class has a Eligible Copy Constructor from myclass }; int main() { my_otherclass class1; class1.param=100; std::cout << class1.param << '\n' ; // Copy Class1 to Class2 by using Copy Constructor my_otherclass class2(class1); std::cout << class2.param << '\n' ; getchar(); return 0; } |
