OOP in C: Vehicle, Car, and Bike Classes

Overview

This project demonstrates object-oriented programming (OOP) principles implemented in C. It introduces a Vehicle base class with three derived classes: Car, Bike and BMW. The implementation follows the fundamental OOP principles of encapsulation, inheritance, and polymorphism while avoiding dynamic memory allocation for instances.

Limitations

This project is a simple educational demo only. The code might have many issues: missing NULL ptr checks before dereferencing, no error handlings, English grammar errors or typos. Its goal is to provides a big picture on one of the ways to implement OOP in C.

Features

• Encapsulation: Grouping attributes and methods inside objects.
• Inheritance: Car and Bike inherit from Vehicle. BMW inherits from Car.
• Polymorphism: Methods in derived classes override base class methods.
• Static Allocation: No dynamic memory allocation.

Repository Structure

├── src/
│   ├── vehicle.c
│   ├── car.c
│   ├── bike.c
│   ├── bmw.c
│
├── include/
│   ├── vehicle.h
│   ├── car.h
│   ├── bike.h
│   ├── bmw.h
│   ├── macros.h
│
├── main.c
├── CMakeLists.txt
└── README.md

Usage

Build the Project

git clone https://github.com/bborovskij/oop_in_c.git
cd oop_in_c/
mkdir build/
cd build/
cmake .. # 'cmake -DCMAKE_BUILD_TYPE=Debug ..' if gdb needed
make

Run the Program

./oop_vehicle

Implementation Details

Base Class: Vehicle

The Vehicle class encapsulates common functionality:

• Attributes: Fuel type, name, number of wheels, and seats.
• Methods: init(), deinit(), start(), stop(), and log().
• Maintains an internal state variable _engine_started.
• Uses virtual method table per object, but in our case, we only store overrided or new methods in object VTable.
• for convenience, use macros to initialize parent object and call any (local or parent) object methods.

Derived Class: Car

Additional attributes and methods:

• New Attribute: doors.
• Overridden Methods: init(), deinit().
• New Method: open_door().

Derived Class: Bike

A simplified derived class:

• Overrides init() to set default values (always 2 wheels and 2 seats).
• Inherits most behavior from Vehicle.

Derived Class: BMW

A simplified derived class:

• Overrides init() and start().
• Inherits most behavior from Car.

Instantiate and use object

1. Call init(&obj) method to instantiate object.
2. Call any object public methods available in respective header.
3. Call deinit() method to clean up the instance.

Example Usage in main.c

#include <stdio.h>
#include <stdbool.h>

#include "car.h"
#include "bike.h"
#include "bmw.h"
#include <string.h>

int main() {
    car my_car = {0};
    car_init(&my_car, "diesel", "any car", 4, 5, 4);
    car_start(&my_car);
    car_stop(&my_car);
    car_deinit(&my_car);
    printf("car cleaned=%d\n", 0==memcmp(&my_car, &(car){0}, sizeof(my_car)));

    printf("\n");

    bike my_bike = {0};
    bike_init(&my_bike);
    bike_start(&my_bike);
    bike_stop(&my_bike);
    bike_deinit(&my_bike);
    printf("bike cleaned=%d\n", 0==memcmp(&my_bike, &(bike){0}, sizeof(my_bike)));

    printf("\n");

    bmw my_bmw = {0};
    bmw_init(&my_bmw);
    bmw_start(&my_bmw, true);
    bmw_stop(&my_bmw);
    bmw_deinit(&my_bmw);
    printf("bmw cleaned=%d\n", 0==memcmp(&my_bmw, &(bmw){0}, sizeof(my_bmw)));

    return 0;
}

Output:

[any car] DEBUG: initiated vehicle running with diesel with 4 wheels and 5 seats
[any car] INFO: Initiated
[any car] DEBUG: vehicle running on diesel stopped
[any car] DEBUG: vehicle running on diesel started
[any car] INFO: De-Initiated
[any car] DEBUG: de-initing vehicle
car cleaned=1

[my bike] DEBUG: initiated vehicle running with gasoline with 2 wheels and 2 seats
[my bike] INFO: Initiated
[my bike] DEBUG: vehicle running on gasoline started
[my bike] DEBUG: vehicle running on gasoline stopped
[my bike] DEBUG: de-initing vehicle
bike cleaned=1

[my bmw] DEBUG: initiated vehicle running with gasoline with 4 wheels and 2 seats
[my bmw] INFO: Initiated
[my bmw] INFO: Inited
[my bmw] DEBUG: vehicle running on gasoline started
[my bmw] INFO: Started in sport mode 1
[my bmw] DEBUG: vehicle running on gasoline stopped
[my bmw] INFO: De-Initiated
[my bmw] DEBUG: de-initing vehicle
bmw cleaned=1

---

Author: bborovskij@gmail.com

License

MIT