Failure INSIDE malloc() ??

[H Phil Duby]

In article <677448705 at macbeth.cs.duke.edu> lsn at duke.cs.duke.edu (Lars S. Nyland) writes:
> I have found over the years that failures that appear to
> be inside of malloc() usually have to do with corrupt data
> structures.  How do they get corrupted?  Not by malloc, not
> usually anyway.
>
> Usually, like many other bugs in C, some pointer has gone
> astray, and you have used it, assigned values to its location,
> and ruined malloc's data structures.
>
> I would bet that you still use a pointer after you have freed
> the memory it points to.  You might amend your free statements
> to be more like:
>       free(p); p = NULL;
> just to make sure that you don't use the pointers after you have
> freed them.
Setting a pointer to NULL does not (at least on some systems) prevent it
from being used.  On my AMIGA, NULL <IS> zero, and is a valid memory
location. There are <run time> tools that detect (and repair) accesses
(especially modifications) to the low memory locations, but this does not
prevent a program from <attempting> to use that memory.  The offending
program is not normally affected, and is usually not even known, except
from the context of what programs are concurrently running.

H. Phil Duby                     uunet!keyword!calgary!ajfcal!mtroyal!phd!phil
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