Out-of-bounds pointers

[Doug Gwyn]

In article <217 at bbxsda.UUCP> scott at bbxsda.UUCP (Scott Amspoker) writes:
-my_proc()
-   {
-   register char *p;
-   p = (char*)malloc(1000);
-   free(p);  /* free never returns but core dumps instead - why? */
-   }
-This seemingly innocent code could possibly error out according to the
-"rules of comformance" presented by some readers.

NO NO NO.  You have mispresented the argument.  So long as malloc()
(assumed to be properly declared!) doesn't return a null pointer,
the above will work in ALL conforming implementations.  The trouble
arises only when after the free() the pointer p (NOT what it points
to, that's inarguably invalid) continues to be examined or otherwise
manipulated by the program.

-Don't worry - all is not lost.  No one was able to come up with a real
-world example of something like this.  In other words - standards and
-ANSI drafts aside - you probably will not get into trouble unless you
-actually try to *de-reference* a bad pointer.

Nobody came up with YOUR example, but there were several examples
posted of genuine computer architectures where continued access of
an invalid pointer value would cause problems.