delete

**Victor Bazarov** · Nov 6 '07, 06:15 PM

Re: delete

Christopher wrote:

If I call delete on a pointer is it guarenteed to set that pointer to
NULL on all implementations ?

Of course not. It's not supposed to do that. I know of no compiler
that would actually do that.

I've also seen "delete this" in a reference counting pointer
implementation and am wondering what the effects of that are.

The effects of 'delete' is calling the destructor and freeing the
memory (usually).

V
--
Please remove capital 'A's when replying by e-mail
I do not respond to top-posted replies, please don't ask

**Joe Greer** · Nov 6 '07, 06:45 PM

Re: delete

Christopher <cpisz@austin.r r.comwrote in news:1194372582 .668032.83740
@y27g2000pre.go oglegroups.com:

If I call delete on a pointer is it guarenteed to set that pointer to
NULL on all implementations ?

Pretty much, its guaranteed not to set the pointer to NULL.

>
I've also seen "delete this" in a reference counting pointer
implementation and am wondering what the effects of that are.
>

Yes, delete calls the destructor on the object and returns the memory to
the available memory pool. It doesn't have any magic way to find all the
pointers to the released memory and NULL them though.

joe

**Scott McPhillips [MVP]** · Nov 6 '07, 06:45 PM

Re: delete

"Christophe r" <cpisz@austin.r r.comwrote in message
news:1194372582 .668032.83740@y 27g2000pre.goog legroups.com...

If I call delete on a pointer is it guarenteed to set that pointer to
NULL on all implementations ?

Nope. But it would be a real good idea to follow your delete by setting
that pointer to NULL yourself. This will help you catch (mis)use of a
deleted pointer during debugging.

--
Scott McPhillips [VC++ MVP]

**Pete Becker** · Nov 6 '07, 07:55 PM

Re: delete

On 2007-11-06 13:39:54 -0500, "Scott McPhillips [MVP]"
<org-dot-mvps-at-scottmcpsaid:

"Christophe r" <cpisz@austin.r r.comwrote in message
news:1194372582 .668032.83740@y 27g2000pre.goog legroups.com...

>If I call delete on a pointer is it guarenteed to set that pointer to
>NULL on all implementations ?

>
>
Nope. But it would be a real good idea to follow your delete by
setting that pointer to NULL yourself. This will help you catch
(mis)use of a deleted pointer during debugging.

The benefits from doing this are mostly illusory.

~MyType()
{
delete my_member_ptr;
my_member_ptr = 0; // silly
}

void delete_it(T *ptr)
{
delete ptr;
ptr = 0; // silly, and doesn't affect the pointer that was used to call
this function
}

That's not to say that setting pointers to NULL is never useful, but it
should be done as part of an overall design, not as a hack that may or
may not help during debugging.

--
Pete
Roundhouse Consulting, Ltd. (www.versatilecoding.com) Author of "The
Standard C++ Library Extensions: a Tutorial and Reference
(www.petebecker.com/tr1book)

**peter koch** · Nov 6 '07, 09:15 PM

Re: delete

On 6 Nov., 19:39, "Scott McPhillips [MVP]" <org-dot-mvps-at-scottmcp>
wrote:

"Christophe r" <cp...@austin.r r.comwrote in message
>
news:1194372582 .668032.83740@y 27g2000pre.goog legroups.com...
>

If I call delete on a pointer is it guarenteed to set that pointer to
NULL on all implementations ?

>
Nope. But it would be a real good idea to follow your delete by setting
that pointer to NULL yourself. This will help you catch (mis)use of a
deleted pointer during debugging.
>
--
Scott McPhillips [VC++ MVP]

I don't think so. I could imagine setting the pointer to some
(nonportable) value, that when accessed would generate a hardware
exception could be a good idea when debugging, but setting it to a
"legal" value should be done only in cases where it really is the
right decision.

/Peter

**ManicQin** · Nov 7 '07, 12:15 PM

Re: delete

The benefits from doing this are mostly illusory.

>
~MyType()
{
delete my_member_ptr;
my_member_ptr = 0; // silly
>
}
>
void delete_it(T *ptr)
{
delete ptr;
ptr = 0; // silly, and doesn't affect the pointer that was used to call
this function
>
}
>

maybe in the dTor it's silly
but beside debug related issues, the code
if (NULL == ptr)
is quite common... IMHO it's always better to nullify the ptr after
deleting him

**Ron Natalie** · Nov 7 '07, 12:25 PM

Re: delete

peter koch wrote:

>>

>>If I call delete on a pointer is it guarenteed to set that pointer to
>>NULL on all implementations ?

>Nope. But it would be a real good idea to follow your delete by setting
>that pointer to NULL yourself. This will help you catch (mis)use of a
>deleted pointer during debugging.
>>
>--
>Scott McPhillips [VC++ MVP]

I don't think so. I could imagine setting the pointer to some
(nonportable) value, that when accessed would generate a hardware
exception could be a good idea when debugging, but setting it to a
"legal" value should be done only in cases where it really is the
right decision.
>
>

Nothing says that the pointer passed to delete is the only copy of
that value in the program (the argument to delete isn't even necessarily
an l-value).

There are debug systems that do try to poison the memory to detect
future references (they do this by usually by not reissuing the same
memory). The C language folk envisioned the ability to also poison
the pointer value (although I know of no system that does this) which
is using an previously deleted pointer value is undefined behavior even
if you don't dereference it.

**Pete Becker** · Nov 7 '07, 12:55 PM

Re: delete

On 2007-11-07 07:14:42 -0500, ManicQin <ManicQin@gmail .comsaid:

>The benefits from doing this are mostly illusory.
>>
>~MyType()
>{
>delete my_member_ptr;
>my_member_pt r = 0; // silly
>>
>}
>>
>void delete_it(T *ptr)
>{
>delete ptr;
>ptr = 0; // silly, and doesn't affect the pointer that was used to call
>this function
>>
>}
>>

>
maybe in the dTor it's silly
but beside debug related issues, the code
if (NULL == ptr)
is quite common... IMHO it's always better to nullify the ptr after
deleting him

As I said in the part you snipped, "That's not to say that setting
pointers to NULL is never useful, but it should be done as part of an
overall design..."

--
Pete
Roundhouse Consulting, Ltd. (www.versatilecoding.com) Author of "The
Standard C++ Library Extensions: a Tutorial and Reference
(www.petebecker.com/tr1book)

**terminator** · Nov 7 '07, 04:25 PM

Re: delete

On Nov 6, 9:09 pm, Christopher <cp...@austin.r r.comwrote:

If I call delete on a pointer is it guarenteed to set that pointer to
NULL on all implementations ?

I thought that pointers are normally passed by value to 'delete',So I
doubt that any delete operator sets its operand to NULL.

I've also seen "delete this" in a reference counting pointer
implementation and am wondering what the effects of that are.

I do not code that way.

regards,
FM.

delete

delete

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