Polymorphism in C

Polymorphism in C.md

#Polymorphism in C

##Summary

C is the lengua franca of embedded development. It is incredibly flexible, with built-in language features for imperative, functional, and object-oriented programming. However, getting inheritance to work effectively in standard C requires a little boiler-plate code, of which I've provided an example here.

base.c

#include <stdlib.h>
#include "base.h"

Base *Base_New(void)
{
  return (Base *)malloc(sizeof(Base));
}

void Base_Delete(Base *baseObject)
{
  free(baseObject);  
}

base.h

#ifndef BASE_H
#define BASE_H

typedef struct _BASE
{
  int baseParameter;
} Base;

Base *Base_New(void);
void Base_Delete(Base *baseObject);

#endif

main.c

#include <stdio.h>
#include "sub_class.h"

int main()
{
  Base *baseObject;
  SubClass *subClassObject;

  subClassObject = SubClass_New();
  subClassObject->otherParameter = 5;
  subClassObject->base->baseParameter = 3;
  printf("The sub-class object's baseParameter value is %d\n", subClassObject->base->baseParameter);

  baseObject = subClassObject->base;
  printf("The baseParameter value after casting to the base class is %d\n", baseObject->baseParameter);

  baseObject->baseParameter = 5;
  printf("Updated baseParameter to %d\n", baseObject->baseParameter);
  printf("The sub-class baseParameter value is now %d\n", subClassObject->base->baseParameter);

  SubClass_Delete(subClassObject);
  return 0;
}

Makefile

build: 
	gcc -g -o obj/base.o -c base.c
	gcc -g -o obj/sub_class.o -c sub_class.c
	gcc -g -o obj/main.o -c main.c
	gcc -g -o main.exe obj/main.o obj/sub_class.o obj/base.o

run: build
	./main.exe

all: run

sub_class.c

#include <stdlib.h>
#include "sub_class.h"

SubClass *SubClass_New(void)
{
  Base *base = Base_New();
  SubClass *sub = (SubClass *)malloc(sizeof(SubClass));
  sub->base = base;
  return sub;
}

void SubClass_Delete(SubClass *subClassObject)
{
  Base_Delete(subClassObject->base);
  free(subClassObject);
}

sub_class.h

#ifndef SUB_CLASS_H
#define SUB_CLASS_H

#include "base.h"

typedef struct _SUB_CLASS
{
  Base *base;
  int otherParameter;
} SubClass;

SubClass *SubClass_New(void);
void SubClass_Delete(SubClass *subClassObject);

#endif