[postgis-devel] getPoint_internal dangerous?

[Paul Ramsey]

It's not a struct alignment thing (anymore) but there is a danger in
mutating the point array storage directly, because in the database context
it's not clear who owns it, and we've had problems in the past w/ functions
that directly write into the database storage. If you're going to be
changing data, the safest thing is always to take a copy at the start.

P.

On Mon, Mar 6, 2017 at 12:25 PM, Björn Harrtell <bjorn.harrtell at gmail.com>
wrote:

> I want to mutate one axis of the points in a POINTARRAY in the most
> efficient way.
>
> Something similar to ptarray_longitude_shift, see:
> https://github.com/postgis/postgis/blob/svn-trunk/
> liblwgeom/ptarray.c#L1393
>
> I see memcpy being used there and other places and afaik it has something
> to do with fears of struct misalignment.
>
> Does this mean I should most definitely not do this? :)
>
> POINT2D *p = (POINT2D *) getPoint_internal(pa, 0);
> p->y = extent - p->y;
>
> Regards,
> Björn
>
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