Re: Right way to delete a pointer [modified] - C / C++ / MFC Discussion Boards

Re: Migrating from VC6 to VS2005 [modified]

C^hris L^osinger2-Jun-06 1:58

C^hris L^osinger

2-Jun-06 1:58

Obliterator wrote:
function declaration is not aware of which list the iterator belongs.

does the function itself know ? if not, how do you know the iterator is valid ? (can't test against vec.end() if you don't have the vector)

a quick run through Google tells me that it's not possible, in general, to set iterators to NULL. iterators are not pointers, for one thing.

i think you'll need to re-work that function a bit

Cleek | Image Toolkits | Thumbnail maker

Re: Migrating from VC6 to VS2005 [modified]

Obliterator2-Jun-06 2:17

Obliterator

2-Jun-06 2:17

Good point. Actually, I simplified the function declaration for the purposes of the queston. The end vector is also supplied as a parameter to the function.

However, the function is indeed aware of the list and simply defaults to the beginning of the list if itStartPos parameter is NULL.

I guess your right - I'm going to have to drop the default parameter here and update each call to the function. Serves me right for using a hack to assign NULL to it in the first place. Damn this new strict checking!!!

Thanks for your response. Much appreciated.

--

The Obliterator

Re: Migrating from VC6 to VS2005

Michael Dunn2-Jun-06 7:46

Michael Dunn

2-Jun-06 7:46

Starting with VC7, STL iterators were type-checked better. You can't treat a collection<T>::iterator as a T* (or any other pointer value, like NULL).

--Mike--
Visual C++ MVP Cool | :cool:

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Re: Migrating from VC6 to VS2005

Obliterator9-Jun-06 2:33

Obliterator

9-Jun-06 2:33

So I see. This is causing me some real headaches!!!
Is there no assignement that can be made to the iterator which means its invalid?

I used to assign NULL to iterators to mean they wern't being used.
Then I could simply check its NULL status and act accordingly.

There must be a way of saying an iterator is invalid.
If I assign it the value of vectorlist.end() I could test against that - but does initial end assignment remain valid after things are added to the vector list?

--

The Obliterator

Right way to delete a pointer

zahid_ash2-Jun-06 1:31

zahid_ash

2-Jun-06 1:31

CSocket * sock;

is it a right way to delete a pointer

sock = NULL;
delete sock;

Or can I directly do

delete sock;

Regards.

Re: Right way to delete a pointer

Cedric Moonen2-Jun-06 1:40

Cedric Moonen

2-Jun-06 1:40

zahid_ash wrote:
sock = NULL;
delete sock;

This won't do anything !
You first have to delete the pointer THEN set it to NULL:

delete sock;
sock = NULL;

Cédric Moonen
Software developer

Charting control

Re: Right way to delete a pointer

Amar Sutar2-Jun-06 1:41

Amar Sutar

2-Jun-06 1:41

CSocket* pSocket;

// Allocate a memory for pSocket

// Delete a allocated memory
if(pSocket)
{
delete pSocket;
pSocket = NULL;
}

Regards
Amar. Smile | :)

Re: Right way to delete a pointer [modified]

Viorel.2-Jun-06 2:14

Viorel.

2-Jun-06 2:14

I think you can even skip the checking for NULL:

delete pSocket; // without redundant "if(pSocket != NULL) ..."
pSocket = NULL;

This is because delete operator performs itself a test for null pointers. You only have to be sure that pSocked was properly initialized before with a right value or with NULL.

-- modified at 9:42 Friday 2nd June, 2006

Re: Right way to delete a pointer [modified]

Zac Howland2-Jun-06 3:50

Zac Howland

2-Jun-06 3:50

Viorel Bejan wrote:
This is because delete operator performs itself a test for null pointers. You only have to be sure that pSocked was properly initialized before with a right value or with NULL.

This only happens in debug builds. You should ALWAYS check for null before deleting a pointer. Calling delete NULL has undefined behavior and should be avoided.

If you decide to become a software engineer, you are signing up to have a 1/2" piece of silicon tell you exactly how stupid you really are for 8 hours a day, 5 days a week

Zac

Re: Right way to delete a pointer [modified]

Nish Nishant2-Jun-06 3:54

Nish Nishant

2-Jun-06 3:54

Zac Howland wrote:
This only happens in debug builds. You should ALWAYS check for null before deleting a pointer. Calling delete NULL has undefined behavior and should be avoided.

That's not true, Zac.

See 16.8 on http://www.parashift.com/c++-faq-lite/freestore-mgmt.html[^]

Regards,
Nish

Nish’s thoughts on MFC, C++/CLI and .NET (my blog)
Currently working on C++/CLI in Action for Manning Publications.
Also visit the Ultimate Toolbox blog (New)

Re: Right way to delete a pointer [modified]

Zac Howland2-Jun-06 4:58

Zac Howland

2-Jun-06 4:58

Yes, the standard says that. However, most compilers did not meet that standard until recently (and some still don't). It is one of those better safe than sorry things.

If you decide to become a software engineer, you are signing up to have a 1/2" piece of silicon tell you exactly how stupid you really are for 8 hours a day, 5 days a week

Zac

Re: Right way to delete a pointer [modified]

Nemanja Trifunovic2-Jun-06 6:17

Nemanja Trifunovic

2-Jun-06 6:17

Zac Howland wrote:
However, most compilers did not meet that standard until recently (and some still don't). It is one of those better safe than sorry things.

Compilers don't meet the Standard mostly in some areas of template handling. Deleting a zero is perfectly safe and has been for quite a while.

My programming blahblahblah blog. If you ever find anything useful here, please let me know to remove it.

Re: Right way to delete a pointer [modified]

Zac Howland2-Jun-06 8:09

Zac Howland

2-Jun-06 8:09

Nemanja Trifunovic wrote:
Compilers don't meet the Standard mostly in some areas of template handling. Deleting a zero is perfectly safe and has been for quite a while.

Let me put it this way ...

There is a reason why the DirectX libraries define the following macro:

#define SAFE_DELETE(p) if(p) { delete p; p = NULL; }

If you decide to become a software engineer, you are signing up to have a 1/2" piece of silicon tell you exactly how stupid you really are for 8 hours a day, 5 days a week

Zac

Re: Right way to delete a pointer

Nemanja Trifunovic2-Jun-06 12:50

Nemanja Trifunovic

2-Jun-06 12:50

Zac Howland wrote:
There is a reason why the DirectX libraries define the following macro

Yep, there is: Microsoft DirectX programmers don't know C++ very well. Poke tongue | ;-P

My programming blahblahblah blog. If you ever find anything useful here, please let me know to remove it.

Re: Right way to delete a pointer [modified]

Nemanja Trifunovic2-Jun-06 4:48

Nemanja Trifunovic

2-Jun-06 4:48

Zac Howland wrote:
Calling delete NULL has undefined behavior and should be avoided.

Nope, delete NULL is required by the C++ Standard to do nothing.

It is perfectly safe.

My programming blahblahblah blog. If you ever find anything useful here, please let me know to remove it.

Re: Right way to delete a pointer

SteveKing2-Jun-06 3:40

SteveKing

2-Jun-06 3:40

Always NULL the pointer after deleting it. Otherwise you could (if you're not very, very careful) try to delete the same pointer twice, which will result in an access violation.
Deleting a NULL pointer however is perfectly safe.

Re: Right way to delete a pointer

James R. Twine2-Jun-06 4:39

James R. Twine

2-Jun-06 4:39

Another reason for doing that is that the address used for the recently-deallocated memory may still be valid in your address space and while not technically valid for use, accessing it might not cause an IPF or Access Violation. For example:

TCHAR *pcBuffer = new TCHAR[ 1024 ];
 
delete [] pcBuffer;
pcBuffer[ 1 ] = _T( 'A' );

   The above code may not crash even though the pointer is technically invalid.

  By setting it to NULL, you just about guarantee that accessing it will cause an Access Violation (at least if on Win32 and if the access range of the pointer is < 4096, because that hits the reserved "NULL pointer page" which causes an instant exception, IIRC).

   Peace!

-=- James

If you think it costs a lot to do it right, just wait until you find out how much it costs to do it wrong!
Avoid driving a vehicle taller than you and remember that Professional Driver on Closed Course does not mean your Dumb Ass on a Public Road!
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Current directory

racing572-Jun-06 1:30

racing57

2-Jun-06 1:30

Can anyone tell me the function call to get the path of the application... i cant for the life of me remember..

Thanks
Lee

Re: Current directory

Hamid_RT2-Jun-06 1:32

Hamid_RT

2-Jun-06 1:32