Function overriding in C

Question

I have a requirement in C similar to function overriding. I have 2 devices with different device IDs. I have a process which just calls device_create(device_id). The process doesn't know which device_create to call. It is upto driver of the device to execute device_create if the device_id matches to driver's device Id. Is there any way to do it in C?

Answer 1

If you use different shared objects (or dlls) to implement the function you could handle this programatically on your own. You could create a plugin like structure and use something like the Command pattern.

Not exactly simple, but can help with your problem.

Cheers.

Answer 2

OK. Understand I'm still of the mark, but leave this post for now.

You do not know the ID when process starts. When HW is attached you read the ID and want to call correct function based on the ID but without using the ID directly?

The closest I can think of as a simple solution is by using an array of function pointers:

void (*funs[3])(void) = {
        &device_create100,
        &device_create200,
        NULL
};

But then only if you can normalize the ID to match index of the array. Say all ID's are in the range 1000-1032 that would be an 32 long function pointer array where you can use ID - 1000.

As this is rather unlikely you could resort to a sorted list, binary tree, hash table or the like on which you do a lookup.

struct node {
    int (*fun)(void);
    int id;
    struct *node left;
    struct *node right;
}

This is of course then assuming you have a rather big list of possible ID's and a switch is out of the question.

---

Old post.

What about function pointers:

int (*device_create)(int);

int device_create_init(int id)
{
     switch (id) {
     case 0x0a:
           device_create = &device_create_100;
           break;
     case 0x0b:
           device_create = &device_create_200;
           break;
     }
   /* After first call, the now set device_create_xxx function will be 
      invoked on device_create() */
     return device_create(id);
}


int main(void) 
{
     device_create = &device_create_init;

     /* Loop */

     return 0;
}