A class that cannot be instantiated is a(n) _____ .
The classes which cannot be instantiated are referred as “abstract base class”.
Explanation of Solution
Inheritance:
Inheritance is the concept of inheriting the members and properties of a base class from the derived class. The main advantages of inheritance are,
- Code reusability and fast implementation.
- Reduces the program code.
Abstract base class:
Abstract base class is a class which contains at least one pure virtual function.
- Compiler will not permit the user to instantiate an abstract class.
- Normally, in function the base class contains the implementation and the derived class overrides this implementation with its own implementation.
- But, the class which inherits an abstract base class must provide definition to the pure virtual function.
- The pure virtual functions implementation is not provided, and the function can be made pure virtual by adding (= 0) at the end of the function.
- The pure virtual function is mostly implemented in the derived class and not in a base class.
Example for abstract base class with virtual function:
/*Abstract base class as it uses virtual function*/
class Base
{
/*Access specifier*/
public:
/*virtual function*/
virtual void disp() = 0
};
/*Virtual function definition*/
void Base::disp()
{
//statement;
}
Explanation:
In the above example,
- Define the abstract base class with the name of “Base”.
- Declare the pure virtual function with the name of “disp()” to make the class as the abstract class.
- The implementation of pure virtual function “disp()” is not provided in base class. But, it is given outside of the class definition.
- Hence, the abstract base class “Base” cannot be instantiated.
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