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From Martin Sebor <se...@roguewave.com>
Subject Re: problem in temp_buffer
Date Thu, 27 Jul 2006 17:50:16 GMT
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

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