Thread: Object oriented approach in C.

Hi all,

I'm working on object-oriented "approach" in C (using gcc v 3.4.2). I'm using function pointers in structures and static functions. Now I want to experiment on polymorphism. Can anybody plz tell me how I can achieve that? If anybody can throw light upon some other aspect he/she is welcome.

I know that C and C++ compilers are different. Plz don't post answers like "it can never be achieved". I don't need one-to-one mapping.

Thanks n regards,

Arun

Here's my ten-minute attempt:

Code:

#include <stdio.h>

/* Declare the shape object. */
struct shape;

struct ShapeVtbl
{
	void (*Draw)(struct shape*);
	void (*Eat)(struct shape*);
};

struct shape
{
	const struct ShapeVtbl* vtbl; /* Points to the functions for this object,
	                                 which may be a circle or square. */
};

/* Functions which implement a circle object. */
void CircleDraw(struct shape* circle)
{
	printf("Drawing a circle.\n");
}

void CircleEat(struct shape* circle)
{
	printf("Mmm, circles! Doh!\n");
}

CircleCreate(struct shape* circle)
{
	static const struct ShapeVtbl CircleVtbl = { CircleDraw, CircleEat };
	circle->vtbl = &CircleVtbl;
}

/* Functions which implement a square object. */
void SquareDraw(struct shape* square)
{
	printf("Drawing a square.\n");
}

void SquareEat(struct shape* square)
{
	printf("This is going to be painful tomorrow!\n");
}

SquareCreate(struct shape* square)
{
	static const struct ShapeVtbl SquareVtbl = { SquareDraw, SquareEat };
	square->vtbl = &SquareVtbl;
}


int main(void)
{
	int i;

	/* Declare objects. */
	struct shape Shapes[2];

	/* Create objects. */
	CircleCreate(&Shapes[0]);
	SquareCreate(&Shapes[1]);
	
	for (i = 0; i < 2; i++)
	{
		Shapes[i].vtbl->Eat(&Shapes[i]);
		Shapes[i].vtbl->Draw(&Shapes[i]);
	}

	getchar();
	return 0;
}

Hi!

Thanks to both of u. Both the replys were of much help to me.

And sorry for posting the same query in two boards. I'm new here and was unaware of the regulations of the forum.

Regards,

Arun