Abstract Classes

Overview

An Abstract Class is an interface. It forces derived classes to implement certain functions. It is created by placing at least one Pure Virtual Function (`= 0`) inside the class.

Syntax

cpp

class Shape {
public:
    // Pure Virtual Function (= 0)
    virtual void draw() = 0; 
};

// You CANNOT instantiate Shape:
// Shape s; // ERROR!

class Circle : public Shape {
public:
    // MUST implement draw, otherwise Circle is also abstract
    void draw() override {
        cout << "Drawing Circle";
    }
};

Common Pitfalls

Forgetting to implement a pure virtual function in a child class, causing mysterious compiler errors stating that the child class cannot be instantiated.

Interview Tips

Abstract classes act as pure interfaces (like `interface` in Java). They define a contract that all child classes must follow.

Real-World Example

Defining a Plugin interface that developers must adhere to.

example

cpp

class IPlugin {
public:
    virtual void initialize() = 0;
    virtual void execute() = 0;
    virtual ~IPlugin() {} // Virtual destructors are mandatory for interfaces
};

class AudioPlugin : public IPlugin {
public:
    void initialize() override { /* Setup audio */ }
    void execute() override { /* Play audio */ }
};

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