How to write a object oriented program using c

ssg14j · 08-09-2005, 05:55 AM

How to write a program using object oreinented concepts in c?
any one know write one simple program...

kimx · 08-09-2005, 06:37 AM

As far as I know you can't write object oreinented programs in c, but I have never used c much.

markhod · 08-09-2005, 07:16 AM

Quote:

Originally posted by ssg14j
How to write a program using object oreinented concepts in c?
any one know write one simple program...

I know you can do it in FORTRAN 90, so probably you can manage it in c too. But in FORTRAN it is painful. Given this, why not just learn c++ which is designed to be used in an OO way?

Mark

aluser · 08-09-2005, 09:03 AM

How easy it is depends on how many OO concepts you need. If you're simply looking for encapsulation, you can do this style:

Code:

/* dog.h */
struct dog;

    /* public methods */
void dog_bark(struct dog *d);
void dog_walk(struct dog *d);
....
/* end dog.h */

/* dog.c */

struct dog {
   int legs;
   ....
};


    /* here are my private methods: */
static void scratch(struct dog *d)
{
    stuff...
}
    /* end private methods */


void dog_bark(struct dog *d)
{
    stuff...
}

void dog_walk(struct dog *d)
{
    stuff....
    scratch(d); /* call to private method */
}

If you need polymorphism, it's easy to include some function pointers in the struct dog, or to include a pointer to a static table of function pointers in the struct dog. (That's more space efficient if dog has more than a couple of public methods.)

If you need single inheritance, you can do that by extending a struct like so:

Code:

struct poodle {
    struct dog d; /* this must be the first thing in the poodle struct! */
    int poofiness;
};

Then you can call the dog_* methods on a poodle by casting a poodle pointer to (struct dog*). If you're doing polymorphism too, you'd change the function pointers in the d field of the poodle before doing anything with it.

I'll try to explain more of whatever parts of this long ass post you find interesting, if any : ) Clearly it would be beneficial to do some OO programming in a language which actually has syntax for it before trying to fake it in C.

mehuljv · 08-10-2005, 09:25 AM

hi,
even u can make some private public variables in one structure using c.

e.g.

// start test1.h

struct test1
{
int x;
};

struct test2;

struct test
{
struct test1 *t1;
struct test2 *t2;
};

// end test1.h

//start test1.c

#include <stdio.h>
#include "test1.h"

int main()
{
struct test *t = (struct test *)malloc(sizeof(struct test));
alloc(t);
fun(t);
t->t1->x = 90;
print(t);
}

//end test1.c

//start test2.h
struct test2
{
int y;
};

//end test2.h

//start test2.c
#include "test1.h"
#include "test2.h"

int alloc(struct test *t)
{
t->t1 = (struct test1 * )malloc(sizeof(struct test1));
t->t2 = (struct test2 *)malloc(sizeof(struct test2));
}

int fun(struct test *t)
{
t->t1->x = 10;
t->t2->y = 20;
}

int print(struct test *t)
{
printf("%d %d\n",t->t1->x,t->t2->y);
}
//end test2.c

Compile prg with gcc test1.c test2.c, from test1.c u can access t->t1->x bt u cant access t->t2->y .... this is somthing like private and public variable bt it is per file..... if u hv any other file which includes both test1.h and test2.h thn it can use both of above vairables.

Mehul.

elyk1212 · 08-10-2005, 09:41 AM

As mentioned before, a struct with function pointers inside used for methods, would be possible.

But why bother? For the all that pain, you should just use C++... Unless this is not an option for some reason, or you are just doing this for academics.

aluser · 08-10-2005, 09:56 AM

Quote:

why bother

My stab at it:

If you're writing a library, it may be more useful as C because both C and C++ programs can easily link to it, not to mention that there are more programmers who understand C well than who understand C++ well.

Gtk+ is fully object oriented and uses a gobject library to describe its OO idioms. Also, the linux kernel makes use of objects with function pointers, so maybe it's a good thing to understand the idiom since it does exist in the wild.