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

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!
DeleteFXPFiles & CheckFavorites (Please rate this post!)

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

See GetModuleFileName

whitesky

Re: Current directory

racing572-Jun-06 1:49

racing57

2-Jun-06 1:49

Thats the one !!!

Thanks

Re: Current directory

Nibu babu thomas2-Jun-06 3:06

Nibu babu thomas

2-Jun-06 3:06

racing57 wrote:
Thats the one !!!

_tgetcwd

Nibu thomas
A Developer

Programming tips[^] My site[^]

Re: Current directory

David Crow2-Jun-06 3:17

David Crow

2-Jun-06 3:17

The current directory and the "path of the application" are not necessarily the same thing. Most requests are for the latter.

"The largest fire starts but with the smallest spark." - David Crow

Package

VinayCool2-Jun-06 1:22

VinayCool

2-Jun-06 1:22

Hi All,

I want to make package for my project, can anyone help me with this..so that i can install in other system.

Regards,
Vinay Charan.

Re: Package

Hamid_RT2-Jun-06 1:40

Hamid_RT

2-Jun-06 1:40

http://www.codeproject.com/tools/EasyInstaller.asp[^]

whitesky

Re: Package

SteveKing2-Jun-06 3:49

SteveKing

2-Jun-06 3:49

You can try one of the following setup packagers (free):
NSIS[^]
WiX[^]

Timers in VC++

Sharath862-Jun-06 1:08

Sharath86

2-Jun-06 1:08

I would be very grateful to anyone who could give me some easy code to tell me how timers can be used in a MFC application in VC++6.0...
MSDN is not that helpful in the matter as i am getting only .NET hits...
I need to be able to call a purticular member function of the dialog class on timer event..

Sharath

Re: Timers in VC++

Amar Sutar2-Jun-06 1:17

Amar Sutar

2-Jun-06 1:17

Links:
http://www.codeproject.com/system/timers_intro.asp#Win32Timers

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/vcmfc98/html/_mfc_cwnd.3a3a.settimer.asp

Amar Smile | :)

Re: Timers in VC++ [modified]

_AnsHUMAN_ 2-Jun-06 1:21

_AnsHUMAN_

2-Jun-06 1:21

Define a timer id
#define ID_MYTIMER 201

Use SetTimer to set and initiate the timer .
SetTimer(ID_MYTIMER,1000,NULL);//1000 is the mseconds

Put your code in the OnTimer function . You can find it using the Class Wizard.
Use KillTimer() to stop the timer
Somethings seem HARD to do, until we know how to do them.
Wink | ;-)

_AnShUmAn_

-- modified at 7:22 Friday 2nd June, 2006

Re: Timers in VC++ [modified]

James R. Twine2-Jun-06 4:50

James R. Twine

2-Jun-06 4:50

   There is one important thing to remember when dealing with Windows timers that people often forget. The SetTimer function returns the ID of the created timer. There is no guarantee that the actual returned ID of the created timer will be the same ID as requested.

   The return value of SetTimer(...) should be used to identify the timer in the timer-handling function and when destroying the timer.

   (Note that the link provided below to http://www.codersource.net/mfc_working_with_timers.html does this correctly, although it does something really stupid in the OnTimer(...) by using dynamically allocated memory for no good reason...)

   Peace!

-=- James

Re: Timers in VC++

Hamid_RT2-Jun-06 1:22

Hamid_RT

2-Jun-06 1:22

See Working with Timers in Visual C++http://www.codersource.net/mfc_working_with_timers.html

whitesky

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