OpenEuphoria

Re: Reallocate() -- is this safe?

• Posted by Robert Craig <rds at RapidEuphoria.com> Oct 13, 2002
• 366 views

Andy Serpa writes:
> If the new block is bigger we will be copying stuff beyond 
> what was in the original block -- might we run up against 
> the "edge" of available memory?  Is that possible, 
> and what will happen?

Yes, it's possible, and you'll get a machine-level exception 
in that case.

> If it is not safe, is there a way to tell how big the 
> original block was without keeping explicit track 
> at allocate()-time?

Every C compiler uses a different implementation of malloc().
Most, but not all, malloc's store the length of the block,
or something similar, in the 4 bytes preceeding the
address returned by malloc(). I think Watcom's malloc (ex, exw)
stores the length of the block plus 5, so Euphoria's allocate()
will currently do the same on DOS and Windows, 
but I don't guarantee that will always be the case.

For portability, you'd be well advised to allocate an extra
4 bytes, and store the length yourself, or keep track of the
length in some variable.

> I don't suppose there is a way to call realloc() 
> directly with some undocumented machine_func()?

No.

Regards,
   Rob Craig
   Rapid Deployment Software
   http://www.RapidEuphoria.com