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How do I delete a pointer (a pointer to an object) ?

Posted on 2003-10-27
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Last Modified: 2010-04-02
Hi C++ experts,

   I have some questions in the following code :
--------------------------------
  class A{
  } ;

  A *p = new A ;
  delete p ;
---------------------------------
  the "delete p" deletes the object "new A", but the pointer p is still there. How do I delete the pointer itself ?
Also, will p be destroyed automatically if it goes out of scope ?
Thanks a lot !!!

meow ...........

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Question by:meow00
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6 Comments
 
LVL 19

Expert Comment

by:Dexstar
ID: 9627835
meow00:

> the "delete p" deletes the object "new A", but the pointer p is still there.
> How do I delete the pointer itself ?
> Also, will p be destroyed automatically if it goes out of scope ?

Yeah, you don't have to "delete" anything unless it is created by "new".  A* p is creating on the stack without "new", so it will just be destroyed when it goes out of scope.  FYI:  You have to "delete p" before p goes out of scope or else there will be no way to delete it.

Hope that helps,
Dex*
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Expert Comment

by:jkr
ID: 9627877
>>How do I delete the pointer itself ?

You mean the value the pointer has?

#define SAFE_DELETE(x) { delete x; x = NULL;}
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Author Comment

by:meow00
ID: 9627892
I see ....
and I am wondering that : is there a certain kind of "destructor" which can be called explicitly to delete the pointer p ? or actually there is no way to do that ? we can only wait until it goes out of scope or the program terminates ?
Thanks a lot !!!
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LVL 1

Author Comment

by:meow00
ID: 9627918
Actually ... I don't mean the value the pointer has, what I mean is the
"pointer variable p " ... I want to destroy it ... thanks.
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Expert Comment

by:fsign21
ID: 9627953
The pointer p itself will be destroyed automatically if it goes out of scope.

The allocated object will be not deallocated if it goes out of scope, unless you call delete p.

We had a similar question recenly:
http://www.experts-exchange.com/Programming/Programming_Languages/Cplusplus/Q_20772740.html
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Dexstar earned 200 total points
ID: 9627960
meow00:

> Actually ... I don't mean the value the pointer has, what I mean is the
> "pointer variable p " ... I want to destroy it ... thanks.

Like I said before.  You can't "destroy it", except to let it fall out of scope.  One way to do is, is to put the use of it inside of {}'s.  Those will tell your compiler to control the scope more tightly.  For example:

void Whatever()
{
     int i = 5;

     {
          int* p = new int;

          *p = i;
   
          delete p;
     } // p will fall out of scope here

     // Try to use p here, and you'll get an error!
}

Dex*
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