[aclug-L] Re: Simple C question (which shows my C ignorance)

[Tom Hull <thull@xxxxxxxxxxx>]

Larry Bottorff wrote:
> 
> I need to delete a member of an array of structure pointers and have the
> new situation reflected minus the one removed. Can I just do
> free(array1[i]), then decrement the index counter, or do I need to shift
> everything down? The members were allocated with malloc, and I'm lost.
> Any ideas?

free(3) frees a buffer previously allocated by malloc() or calloc(), but
does nothing to the pointer itself. it's still in your array, except now
if you reference it you'll get a bug that nobody will want to touch. you
either have to invalidate your pointer (e.g., set it to 0, always checking
to make sure it's non-0 before referencing it), or shift the rest of your
array down. you can use memcpy(3) for the shift down -- it's smart enough
not to trip on itself, and presumably is coded as efficiently as you can
do it. the choice depends on your usage, where you're willing to spend
the time (small time every access to check for 0, vs. larger time to
compact the array on every delete, vs. much larger time if the array
is huge). if none of these solutions are satisfactory, consider another
data structure.

> --
> Larry Bottorff  /  mrprenzl@xxxxxxxxxx  /  316.345.3387

-- 
/*
 *  Tom Hull * thull@xxxxxxxxxxx * http://www.ocston.org/~thull/
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