Mercury, You might be interested in the new-placement optional argument to the new operator. It is defined in section 5.3.4 of the c++ specification. corey On Tue, 8 Mar 2005 12:14:22 -0700, JP Mercury <swirlee@xxxxxxxxxxxx> wrote: > 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 > >
