How Do I Define an Interface in C Using Abstract Base Classes?

Defining an Interface in C

In C , an interface can be declared using an abstract base class (ABC). An ABC is a class with at least one pure virtual method. A pure virtual method is a method that is declared with the keyword = 0.

class IDemo {
public:
    virtual ~IDemo() {}
    virtual void OverrideMe() = 0;
};

In the example above, IDemo is an ABC with a pure virtual method named OverrideMe. Any class that inherits from IDemo must define an implementation for OverrideMe. Otherwise, IDemo can be used to represent an interface that can be implemented by different concrete classes.

class Parent {
public:
    virtual ~Parent();
};

class Child : public Parent, public IDemo {
public:
    virtual void OverrideMe() {
        // Do stuff
    }
};

An exception to the list of pure virtual methods in an interface is to add a virtual destructor. This allows pointer ownership to be passed to another party without exposing the concrete derived class. The destructor doesn't have to do anything since the interface doesn't have any concrete members.

class IDemo {
public:
    virtual ~IDemo() {}
    virtual void OverrideMe() = 0;
};

In conclusion, an interface can be used to represent the abstract properties and methods of a class. By creating an ABC with pure virtual methods, you can ensure that any class inheriting from it must define implementations for the interface methods. Additionally, adding a virtual destructor to the interface can enable safe pointer ownership transfer.

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