C++ · 2 · Classes & RAII7 / 36 · 19%

Inheritance & Polymorphism

virtual functions enable runtime dispatch through a vtable.

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virtual

Override in derived classes and call through a base pointer/reference.

Example

example

struct Shape {
    virtual double area() const = 0;   // pure virtual
    virtual ~Shape() = default;
};
struct Circle : Shape {
    double r;
    Circle(double r) : r(r) {}
    double area() const override { return 3.14159 * r * r; }
};

vtable dispatch

override & final

Ask the compiler to check you actually override.

Example

example

struct D : Shape {
    double area() const override { return 0; }
    // typo like: double are() const override;  → compiler error
};

Virtual Destructor

Base with virtual functions must have virtual dtor, or deletion is UB.

Example

example

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Shape* s = new Circle(2);
delete s;   // needs Shape::~Shape() virtual