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From: David Schwartz <davids@webmaster.com>
Newsgroups: comp.std.c++
Subject: Re: why doesn't delete NULL the pointer?
Date: Fri,  5 Apr 2002 16:49:47 GMT
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Ken Alverson wrote:

> I still feel my analogy is valid, but this really isn't going anywhere, so
> I'll drop the issue.
> 
> Ken

	So what do you do if the value of the pointer is still needed?!

Consider the following code:

Mutex mutex_table[256];

void LockMutex(void *p)
{
 mutex_table[reinterpret_cast<unsigned int>(p)%256].Lock();
}

void UnlockMutex(void *p)
{
 mutex_table[reinterpret_cast<unsigned int>(p)%256].Unlock();
}

void ConditionalLockedDelete(Foo *p)
{
 LockMutex(p);
 if(p->ShouldDelete()) delete p;
 UnlockMutex(p);
}

	How would this work if 'delete' NULLed the pointer? Here's another
case:

class Foo
{
 protected:
 Foo *brother;
 bool can_delete;
 public:
 static bool Detach(Foo *a)
 {
  if(can_delete) { delete a; return true; }
  return false;
 }
 void BrotherNowGone(void) { brother=NULL; }
 Foo *GetBrother() { return brother; }
}

void DetachAndDeLink(Foo *a, Foo *b)
{
 bool did_delete=a->Detach();
 if(did_delete && (b->GetBrother()==a)) b->BrotherNowGone();
}

	How would this work if 'delete' NULLed the pointer?

	DS

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