On Jan 30, 2014, at 12:46 PM, Brad Aagaard <[email protected]> wrote:

On 01/30/2014 10:34 AM, Jed Brown wrote:

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Brad Aagaard <[email protected]> writes:

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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. Barry

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

Brad