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Re: Segfault with delete[] operator & virtually derived classes


Nathan, Eljay, Lyle-

Thanks for your responses. 

> >>you asked for an array of Bs, if you're not treating it as an array of
> >>Bs it's not gonna work.

As far as I know, I can do new B[10]; and store it in any pointer type.
For example:

char *ptr = (char *) new B[10];
C *ptr = (C *) new C[10];

No problem unless I try to dereference ptr, then I will get the wrong data.
But I take the true size of one array element into account and always cast
back to a A * before dereferencing an array element. I don't see this as lying
to the compiler, just a clever use of casting and walking an array. 

I used to do a lot of video coding and we did that all the time, casting video
memory between char * and long * and what not. The memory remains the same, we
just look at it in a different way.

But let's say I take your suggestion and implement an array of pointers. How
do I allocate the memory for 10 Bs in one block? I don't want 10 separate
instances of B, I want a contiguous block of 10 Bs. I could create a block of
10 Bs:

B *block = new B[10];

and then an array of pointers:

A **ptrarray = new A *[10];

and then point the elements in the array to the block--

for (int i = 0; i < 10; i++)
  ptrarray[i] = &block[i];  // Or block+i, whichever you prefer

But then how would I delete the block? I would still have to do:

delete[] block;

and I can't do this because in my code the memory manager (base class) does
not know about the derived classes. delete[] only appears to work when the
pointer type matches the actual type allocated-- in contrast to 'delete',
which works regardless.

Kind Regards,
-Mercury


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