Re: [Firebird-devel] Off by one error?

[Ann W. H. <aha...@ib...>]

At 09:47 PM 12/5/2001 -0800, John Bellardo wrote:
>Hi all,
>         In updating the FB2 code I happened across the find_proc_field in 
> par.c:
>
>list = procedure->prc_output_fields;
>for (ptr = list->vec_object, end = ptr + list->vec_count - 1; ptr < end; 
>ptr++)
>     {
>     param = (PRM) *ptr;
>     if (!strcmp (name, param->prm_name))
>     return param->prm_number;
>     }
>
>
>Notice that we never look at the last field in the vector.  Is this 
>intentional?  If it is we should add a comment to the code because it is 
>unintuitive why (at least for me).


Yes we do.  Assume a vector of three.  O, 1, 2.  vec_count = 3.
vec + vec_count = a place just beyond the last element.  This
mechanism is used all over because in the olden days it produced
better code than the alternatives.  Whenever you see something
of the format

    for (ptr = x, end = x + count; ptr < end; ptr++)

end will be beyond the end of the x structure.

Regards

Ann



Regards,

Ann
www.ibphoenix.com
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