C++Builder Learn about Eligible Default Constructor in C++

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Learn about Eligible Default Constructor in C++
By Yilmaz Yoru June 29, 2021

Do you want to learn what is Eligible Default Constructor or what kind of methods we have that we can declare and use Eligible default constructors? In this post, we will try to explain the Eligible Default Constructor with examples.

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.

class myclass
{         
  public:   
    myclass()
    {
       std::cout << "myclass is constructed!\n";
    };
};

There are different contractor types and the Default Constructor in classes is one of these. This method not only used in classes but also used with struct and union data types.

A Default Constructor is a constructor type in Classes that is called when class is defined with no arguments, or it is defined with an empty parameter list, or with default arguments provided for every parameter. A type with a public default constructor is Default Constructible; There are different methods to use this Default Constructor and one of the terms that we meet sometimes is Eligible Default Constructor. If you are looking for what is Eligible Default Constructor in C++, please read below.

Eligible Default Constructor​

The Eligible Default Constructor is a default constructor which is either user-declared or both implicitly-declared and definable (until C++11). The triviality of eligible default constructors determines if the class is an implicit-lifetime type or if the class is a trivial type.

A default constructor is eligible if only all below are provided,

• it is not deleted (C++11, C++20)
• its associated constraints, if any, are satisfied (C++20)
• no default constructor is more constrained than it (C++20).

Here is an Eligible Default Constructor example,

class myclass
{         
  public:   
    myclass() // Eligible Default Constructor
    {
       std::cout << "myclass is constructed!\n";
    };
};