[petsc-dev] PetscMalloc for size zero

[Matthew Knepley]

On Thu, Jan 30, 2014 at 1:53 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:

>
> On Jan 30, 2014, at 12:46 PM, Brad Aagaard <baagaard at usgs.gov> wrote:
>
> > On 01/30/2014 10:34 AM, Jed Brown wrote:
> >> Brad Aagaard <baagaard at usgs.gov> writes:
> >>
> >>> Matt and Jed,
> >>>
> >>> I see that Jed pushed some changes (jed/malloc-zero) for PetscMalloc to
> >>> deal with memory alignment and a zero size. It looks like the pointer
> >>> will NOT be NULL for a size of 0. Is this true?
> >>
> >> Yes, just like malloc(), it can be either a unique pointer or NULL.  You
> >> need the size anyway to know how many elements are in the array.
> >
> > I thought it was a nice feature that PETSc improved on malloc() and
> free() by returning NULL for zero sized allocation (although this wasn't
> true for --with-debugging=0 due to memory alignment) and set pointers to
> NULL after freeing.
>
>    With PetscMalloc() we could certainly return NULL on 0 mallocs but the
> code is a bit more involved  for the PetscMallocn() case.
>
>    Here is what I suggestion. Someone suggest (i.e.. write) a
> refactorization of PetscMalloc(), PetscMallocn() that handles correctly any
> of the sizes being zero correctly in a branch and see how it goes.


I have pushed it. It looks simple to me

   Matt


>
>    Barry
>
>
> >
> > What is the rationale for not returning NULL for mallocs of size zero
> other than conforming to C malloc behavior?
> >
> > Brad
> >
> >
>
>


-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-dev/attachments/20140130/e3e3c424/attachment.html>