Linked lists and new/delete?

Alot of the tutorials on linked lists that i have gone through lately, uses the new operator to allocate memory for a new node in the list, but never checks if the allocation failed, and they don't use the delete operator to clear the memory afterwards either, this includes the tut on cprogramming.com. Why is that? Is there a particular reason?

Also, i've tried to make a loop to destroy a linked list of mine after usage, but i keep getting segmentation errors when i run it:

Code:

---

while(conductor != NULL)
{
        temp_conductor = conductor->next;
        delete conductor;
        conductor = temp_conductor;
        conductor = conductor->next;
}

---

Conductor is the pointer i'm using to traverse the list, temp_conductor is a similar pointer that i'm using to temporarily hold the value of conductor while i delete the node conductor points to.

My guess is that the line i've highlighted is giving me problems, rather than deleting conductor itself, i wan't to delete the node that conductor is pointing to, how would i go about this?

Edit: I'm an idiot, removed my reply ;P.

Check anons reply.

How about using a recursive function

Code:

---

void DestroyConductor( (type?) *conductor)
{
    if (conductor->next)
        DestroyConductor(conductor->next);
   
    delete conductor;
}

---

Or better not if you happen to have long lists...

Just throw out the conductor = conductor->next as you seem to be advancing twice each iteration.

Quote:

---

Originally Posted by anon

Or better not if you happen to have long lists...

Just throw out the conductor = conductor->next as you seem to be advancing twice each iteration.

---

What a stupid error, i threw out the "conductor = conductor->next" and i am no longer getting seg errors, but how can i be sure that i have deleted the entire list?

Well, if conductor is initially set to head, the deletion of everything should be the logical outcome (or your list is incorrect anyway).

There might be tools to check for memory leaks.

You might also make a list of objects that count the instances and see if the count is 0 after the list gets destructed.

Quote:

---

Originally Posted by anon

Well, if conductor is initially set to head, the deletion of everything should be the logical outcome (or your list is incorrect anyway).

There might be tools to check for memory leaks.

You might also make a list of objects that count the instances and see if the count is 0 after the list gets destructed.

---

Well, i'm sure that my list is correct or otherwise the rest of my program wouldn't be working. Thanks for helping me out Anon :)

Still, why isn't there anything about deleting a linked list in the FAQ?

Prelude's tutorial in the FAQ here has a paragraph on deleting the memory (basically the same thing you do).

Quote:

---

Alot of the tutorials on linked lists that i have gone through lately, uses the new operator to allocate memory for a new node in the list, but never checks if the allocation failed, and they don't use the delete operator to clear the memory afterwards either, this includes the tut on cprogramming.com. Why is that? Is there a particular reason?

---

It is quite annoying and complicated to check everything (new throws an exception, and you might need smart_pointers instead of regular ones to be safe), therefore most tutorials leave error-checking out to keep the focus on the issue at hand.

Not freeing memory might result from just sloppiness.

Quote:

---

Originally Posted by anon

Prelude's tutorial in the FAQ here has a paragraph on deleting the memory (basically the same thing you do).

---

Oh, i didn't realize that, never got around to checking Prelude's corner to be honest, anyways, thanks for the help.

Quote:

---

Originally Posted by Neo1

Also, i've tried to make a loop to destroy a linked list of mine after usage, but i keep getting segmentation errors when i run it:

Code:

---

while(conductor != NULL)
{
        temp_conductor = conductor->next;
        delete conductor;
        conductor = temp_conductor;
        conductor = conductor->next;
}

---

---

One problem with this code is you're calling delete on a pointer that you haven't checked to be NULL. You get a seg fault when you're at the last node in the list and calling delete on the next pointer which is NULL. Also, as pointed out, you're actually traversing 2 nodes each iteration which will cause memory leaks.

Code:

---

IF head != NULL
  WHILE head->next != NULL
      temp = head
      head = head->next
      delete temp
  END WHILE
  delete head
  head = NULL
END IF

---

Something like this I believe should work.

Quote:

---

One problem with this code is you're calling delete on a pointer that you haven't checked to be NULL.

---

No, he doesn't. Due to the while() condition variable 'conductor' cannot be null when delete is called.

Quote:

---

You get a seg fault when you're at the last node in the list and calling delete on the next pointer which is NULL.

---

No he doesn't, deleting null pointers is safe.

The real problem with this code is:

Code:

---

while(conductor != NULL)
{
  temp_conductor = conductor->next; /* If temp_conductor becomes NULL... */
  delete conductor;                /* (delete works anyway) */
  conductor = temp_conductor;      /* conductor becomes NULL too... */
  conductor = conductor->next;      /* so 'conductor->next' = (null)->next = seg fault */
}

---

Quote:

---

Originally Posted by rpet

No, he doesn't. Due to the while() condition variable 'conductor' cannot be null when delete is called.



No he doesn't, deleting null pointers is safe.

The real problem with this code is:

Code:

---

while(conductor != NULL)
{
  temp_conductor = conductor->next; /* If temp_conductor becomes NULL... */
  delete conductor;                /* (delete works anyway) */
  conductor = temp_conductor;      /* conductor becomes NULL too... */
  conductor = conductor->next;      /* so 'conductor->next' = (null)->next = seg fault */
}

---

---

Yup, you're right on all counts. I had a brain fart. Be leery of that pseudo-code for deleting a linked list I posted, I haven't tested it.

If you have valgrind on your system, you can run

Code:

---

valgrind main

---

To detect memory leaks.