Linked list function

Code:

---

void traverse (link h, void (*visit)(link)) {
  if (h == NULL) {
    (*visit)(h);
    traverse(h->next, visit);
  }
}

---

What exactly does that second parameter mean? I have never seen such an argument before.

A pointer to a function.

It might look like:

Code:

---

void myfunction(link x)
{
    return;
}

/* ... */

/* call traverse */
traverse(h, &myfunction);

/* ... */

---

See http://www.newty.de/fpt/index.html

I get your example, because i have used functions that way before.

But I don't get what (*visit)(h) is. Does it mean the function visit is pointing to the h node

One can also write:

Code:

---

traverse(h, myfunction);

---

EDIT:

Quote:

---

But I don't get what (*visit)(h) is. Does it mean the function visit is pointing to the h node

---

visit is a function pointer, so it is just calling the function and passing h as the argument. You can also write visit(h).

Calls what's pointed to by visit with the parameter h.

No need to dereference, it's the same as

Code:

---

visit(h);

---

Basically,

Code:

---

traverse(h, myfunction);        /* short way */
traverse(h, &myfunction);      /* long way */

---

Code:

---

visit(h);                      /* short way */
(*visit)(h);                    /* long way */

---

Both are correct.

Thanks guys.

My lecturer seems intent on confusing people to no end, but then again perhaps it's a good thing I learnt this style of coding. Pretty easy then.

Thanks zacs7 and laserlight =)

Writing the form

Code:

---

(*visit)(h);

---

makes sure that it's CLEAR that visit is a funciton pointer - it's not needed, and I don't use that form when I use function pointers - but it is valid, and offers a slightly higher degree of "explaining what is going on" (assuming of course you can follow it).

--
Mats

Quote:

---

makes sure that it's CLEAR that visit is a funciton pointer - it's not needed, and I don't use that form when I use function pointers - but it is valid, and offers a slightly higher degree of "explaining what is going on" (assuming of course you can follow it).

---

The trade off of this slightly higher degree of explanation is that it delves into the details. I think that taking a typedef and then using "normal" function call syntax makes for a higher level of abstraction instead, e.g.,

Code:

---

typedef void (*VisitFunction)(link);

void traverse(link h, VisitFunction visit) {
  if (h == NULL) {
    visit(h);
    traverse(h->next, visit);
  }
}

---

Incidentally, h == NULL looks like it should be h != NULL instead since h->next would result in the dereferencing of a null pointer if h == NULL.