[petsc-dev] PetscMalloc for size zero

[Jed Brown]

Brad Aagaard <baagaard at usgs.gov> writes:
> 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?

The standard could have easily specified that malloc(0) returns NULL.
It didn't because leaving it unspecified allows better memory-checking
tools (e.g., you can check for matching free even when your tests happen
to allocate 0 bytes).  As you mention, PETSc did not guarantee it either
--with-debugging=0, so correct code cannot depend on it.  We are just
now being explicit that we only make the same guarantees as malloc().

We still set pointers to NULL after freeing.
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