[Numpy-discussion] record descriptors: trailing unused bytes

Martin Wiechert Martin.Wiechert at mpimf-heidelberg.mpg.de
Mon Sep 18 17:12:31 CDT 2006

On Monday 18 September 2006 20:46, Travis Oliphant wrote:
> Martin Wiechert wrote:
> > Hi list,
> >
> > does anybody know, if in C in the PyArray_Descr struct it is safe to
> > manually change descr->elsize and descr->alignment as long as these are
> > compatible and descr->elsize is large enough to hold all fields? Of
> > course I mean before any array is constructed using descr.
> Well, you should really make a copy of the PyArray_Descr structure and
> then fill it in as desired unless you are sure that no other arrays have
> are using that particular data-type object to describe their own data:
> PyArray_DescrNew gives you a new copy based on an old one (you just get
> a reference to the funciton pointers in the 'f' member so don't go
> changing those).
> I guess your statement about "before any array is constructed using
> descr" means you are sure that there are no other arrays using the old
> elsize and alignment.
> Then it should be fine.  There are not supposed to be any assumptions
> about the data-types except for what is explicitly provided in the
> data-type object (PyArray_Descr *).  So, changing them will change the
> data-type and things should ideally work.
> -Travis


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