Nicole Willson wrote:
The problem is simply that the address for last is:
(gdb) print last
$5 = (Header *) 0x77f00008
And the address for ptr (after malloc) is:
(gdb) print ptr
$4 = (void *) 0x77e00d30
Since ptr is
(gdb) print block_size
$1 = 2147483680
The end of the block pointed to by ptr is 0xf7e00d50 - you will note
that last is inside of ptr's block of memory now. Then when memset is
called on ptr setting everything to -1, last's information is
obliterated.
My question now is:
Since last is in the midst of the block allocated to ptr, shouldn't that
allocation have failed?
The allocation should fail if the size of the requested block (nbytes)
is greater than malloc() can find. If it fails, the returned pointer
will be 0. Otherwise the allocated block must not overlap with any
other previously allocated (and not yet deallocated) block. From
what you said it sounds like last might be pointing to an already
deallocated block of memory (which should not happen). If that's
what's happening you'll need to figure out why :)
Martin
