[petsc-users] DMDAVecGetArray vs DMDAVecRestoreArray

[Alan Wei]

Dear Barry,
    Thanks for your reply.

best,
Alan


On Thu, Aug 18, 2011 at 5:49 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:

>
> On Aug 18, 2011, at 5:02 PM, Alan Wei wrote:
>
> > Dear all,
> >     I hope you're having a nice day.
> >     I'm trying to get the x, y-value of a coordinate created by
> DMDACreate2d. Lines I wrote down are:
> >
> >   DMDAGetCoordinateDA(da, &cda);
> >   DMDAGetGhostedCoordinates(da, &gc);
> >   DMDAVecGetArray(cda, gc, &coors);
> >
> >   for (i = xs; i < xs+xm; i++) {
> >     for (j = ys; j < ys+ym; j++) {
> >       printf("%f  %f\n", coors[j][i].x, coors[j][i].y);
> >     }
> >   }
> >
> >   DMDAVecRestoreArray(cda, gc, &coors);
> >
> > I wonder why I need to use "DMDAVecRestoreArray(cda, gc, &coors);" I used
> it because the manual said I need. Actually, I tried to comment it out and
> there is no difference.
> >
> > Thanks,
> > Alan
>
>    The practical reason is you might get memory bleeding if you don't.  The
> philosphical reason is that a call DMDAVecGetArray() or VecGetArray() or
> others is a request to access the internal data structure of an object, the
> object then gives you permission to access that data. the RestoreArray() is
> a statement by you that after this call you will NOT access that data
> directly (without another GetArray call). Imagine if you did
>
>    Barry
>
>
>
>
>
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