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.
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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 is 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;
Do you want to learn how we define a Defaulted Default Constructor Outside of a Class Definition? In the definition of a default Constructor, class_name must name the current class or current instantiation of a class template. It must be a qualified class name when declared at namespace scope or in a friend declaration. Here are examples;
Defaulted Default Constructor Outside of a Class Definition
We can easily default the Default Constructor by using = default; after class name with (); We can also do this outside of a Class Definition. The default statement means that you want to use the compiler-generated version of that function, so you don’t need to specify a body. We can also use = delete to specify that you don’t want the compiler to generate that function automatically.
Syntax,
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class_name :: class_name() = default; |
An example with a class;
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class myclass { public: myclass(); }; myclass::myclass() = default; |
Here is a full example about how to code Defaulted Default Constructor Outside of a Class Definition,
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#include <iostream> class myclass { public: int x = 49; myclass(); }; myclass::myclass() = default; int main() { class myclass test; std::cout << test.x << '\n'; getchar(); return 0; } |
The output will be:
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49 |
