[petsc-dev] PetscMalloc for size zero

[Matthew Knepley]

On Thu, 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.
>
> What is the rationale for not returning NULL for mallocs of size zero
> other than conforming to C malloc behavior?


There is no such thing as "conforming to C malloc", since that WOULD allow
returning NULL in this case.

I think we are doing users a disservice by not enforcing this.

   Matt


>
> 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
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