In C++, an abstract class is a class that cannot be instantiated and is designed to be used as a base class for other classes. An abstract class typically contains one or more pure virtual functions, which are functions that have no implementation in the base class and must be overridden in the derived class.
To define an abstract class in C++, we use the following syntax:
class AbstractClass {
public:
virtual void doSomething() = 0;
};
Here, `AbstractClass` is the name of the abstract class, and `doSomething()` is a pure virtual function. The `= 0` syntax indicates that the function has no implementation in the base class and must be overridden in the derived class.
A derived class that inherits from an abstract class must implement all pure virtual functions in the base class, or it will also be considered an abstract class. For example:
class DerivedClass : public AbstractClass {
public:
void doSomething() {
// implementation of doSomething() in the derived class
}
};
In this example, `DerivedClass` is a derived class that inherits from `AbstractClass`, and it provides an implementation for the `doSomething()` function.
An interface in C++ is similar to an abstract class, but it contains only pure virtual functions and no data members. An interface is used to define a set of functions that a class must implement in order to conform to a specific interface. To define an interface in C++, we can use the same syntax as an abstract class, but with no data members:
class Interface {
public:
virtual void doSomething() = 0;
virtual void doSomethingElse() = 0;
};
Here, `Interface` is the name of the interface, and it contains two pure virtual functions.
A class that implements an interface must provide an implementation for all the pure virtual functions in the interface. For example:
class MyClass : public Interface {
public:
void doSomething() {
// implementation of doSomething() in MyClass
}
void doSomethingElse() {
// implementation of doSomethingElse() in MyClass
}
};
In this example, `MyClass` is a class that implements the `Interface` interface, and it provides an implementation for both the `doSomething()` and `doSomethingElse()` functions.
Interfaces are often used in C++ to define a common set of functionality that can be implemented by multiple classes, allowing these classes to be used interchangeably in certain situations. This is known as polymorphism, and it’s a powerful concept in object-oriented programming.