Re: Basing Pointer Questions

[Hans Boldt <boldt@xxxxxxxxxx>]

Smith, Nelson wrote:
> > > 6.)  Where is the information regarding how much memory has been
> > allocated
> >
> > > to a pointer stored?  Is there an API to get at it?  Maybe if I knew
> > this, I
> >
> > > would be able to determine the answers to the other questions above.
> > Basically, you manage that information yourself.  It is up to you to
> > keep track of which pointers point to valid storage, and how much
> > storage is available for each pointer.
> >
> > Cheers!  Hans
> 	[Smith, Nelson]  How does the system know when you are out of
> bounds?
There are two issues.  First, if you go beyond the bounds of the
space, you get a machine exception.

But the other issue is trickier.  If you allocate, say, 100 bytes of
storage, you could easily add 100 to the basing pointer and point to
the memory just beyond what you've allocated.  This could very well
be within the data space, but of course, might contain something
that you'd better not touch.  Unlike the first case, the machine
isn't going to tell you that you've screwed up something, and you
might not know something is wrong until much later on in your program.

The bottom line is this:  Using dynamic storage allocation and
pointers is tricky, and should be used with the utmost of care if it
can't be at all avoided.

Cheers!  Hans