Why point a pointer to 0 after*** deleting it?

Question

I'm confused about why some people point a pointer (created on the heap earlier) to 0 after deleting it.

For example:

Node* newNode = new Node();

delete newNode;
newNode = 0;    // why?

Why does it matter if a deleted pointer points to 0 or to something else?

This is to act as a warning to anybody reading the code. It's a shorthand way of saying: "treat this code with extra care -- the author probably didn't know or understand RAII or else completely misunderstands object lifetime." — Jerry Coffin, Aug 07 '13 at 04:21

score 5 · Accepted Answer · answered Aug 07 '13 at 04:18

5

This is done so that you'll get an immediate error if you ever accidentally try to use it after it's been deleted. Using a pointer that points to deleted memory may sometimes "work", but crash sometime later. By setting it to NULL, you make sure that it's always a bad pointer to use.

answered Aug 07 '13 at 04:18

Nicol Bolas

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This is incorrect - delete 0; will always work - see http://stackoverflow.com/questions/615355/is-there-any-reason-to-check-for-a-null-pointer-before-deleting or the spec. – Ed Heal Aug 07 '13 at 04:32
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@EdHeal: The answer is fine. It says `Using a pointer` not deleting a pointer. – Jesse Good Aug 07 '13 at 04:37
@JesseGood - Delete a NULL pointer - No problem - it works – Ed Heal Aug 07 '13 at 04:42
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@EdHeal: **Using** a pointer encompasses more than just deleting it. hth – Jesse Good Aug 07 '13 at 04:46
@JesseGood - Setting it to zero after deleting it means that if you inadvertently delete it again it is a noop.That was the trust of the question. – Ed Heal Aug 07 '13 at 04:50
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@EdHeal: The question said nothing about deleting it after setting it to NULL. – Nicol Bolas Aug 07 '13 at 05:08

Saksham · Answer 2 · 2013-08-07T04:23:30.530

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You should make a pointer point it to NULL to make it invalid after deleting so that if you try to accidentally access it, you get an error.

NOTE: Earlier versions of compiler used NULL(which is practically #DEFINE NULL 0) to make pointer invalid. C++11 now has nullptr to make it invalid(which is different from NULL)

edited Aug 07 '13 at 04:23

answered Aug 07 '13 at 04:17

Saksham

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score 0 · Answer 3 · answered Aug 07 '13 at 04:18

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So if further in the code you tried to delete it again you will not get an error.

Just a marker that you have done it!

answered Aug 07 '13 at 04:18

Ed Heal

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Why point a pointer to 0 after*** deleting it?

3 Answers3