Modern C++ and C Alternatives

Polymorphism and Function-Table Dispatch

Dynamic polymorphism lets client code call a common operation while the concrete type supplies its behavior.

What is Polymorphism and Function-Table Dispatch?

Dynamic polymorphism lets client code call a common operation while the concrete type supplies its behavior.

Select behavior through a common interface.

Important points

Understand the C mechanism before comparing the C++ abstraction.
Use RAII and value semantics to express ownership.
Prefer type-safe compile-time abstractions over macros and casts.

C and C++ code examples

Run code →

main.c

#include <stdio.h>

typedef struct Shape Shape;
struct Shape {
    double value;
    double (*area)(const Shape *shape);
};

double square_area(const Shape *shape) {
    return shape->value * shape->value;
}

int main(void) {
    Shape square = {4.0, square_area};
    printf("area=%.1f\n", square.area(&square));
}

Expected output

area=16.0

C++

Run code →

main.cpp

#include <iostream>

struct Shape {
    virtual double area() const = 0;
    virtual ~Shape() = default;
};

struct Square : Shape {
    double side;

    explicit Square(double value) : side(value) {}
    double area() const override { return side * side; }
};

int main() {
    Square square(4);
    const Shape& shape = square;
    std::cout << "area=" << shape.area() << '\n';
}

Expected output

area=16

C and C++ comparison

C builds an explicit object pointer plus function table. C++ virtual functions generate comparable dispatch machinery and use a virtual destructor for safe base-pointer deletion.

C uses naming conventions, callbacks, macros, and explicit context structures.

C++

Language features provide scoped, type-safe, and often zero-overhead abstractions.

Practice exercises

Run both versions, then modify them to observe the different language guarantees.

Write the C mechanism before the C++ abstraction.
Remove manual cleanup with RAII.
Check whether the abstraction adds allocations or virtual dispatch.