On May 9, 2011, at 3:53 PM, Blaise Bourdin wrote:
>>> There are still a bunch a sieve-related open issues (I realize that I email
>>> the tickets to petsc-maint and not petsc-dev) introduced when Mesh, DA and
>>> DM were consolidated, and after the XXXDestroy calling
>>> 2. Alternatively, one can implement the options management in C and use
>>> PetscBag to convert data from a fortran derived type to a C struct and
>>> back. One limitation is that enums again are not supported, but neither are
>>> arrays.
>>> 3. If neither 1. or 2. is feasible, would it be possible to add fortran
>>> support for PetscOptionsGetEnum. Assuming that we use a integer for the
>>> enum in fortran, my understanding is that all it would take would be to be
>>> able to pass an array of fortran strings as the list argument of
>>> PetscOptionsGetEnum.
>>
>> This is the crux of the matter. We don't have any portable way of passing
>> an array of strings from Fortran to C. (Portably passing a single string is
>> bad enough). If someone figures out how, using the Fortran 2003 standard for
>> passing arguments to/from C, to handle arrays of strings (assuming the
>> standard supports it) then we could provide PetscOptionsGetEnum() for
>> Fortran 2003, but that would be a user contribution, we're not going to do
>> the work ourselves.
>
> I am attaching an example doing exactly that and illustrates how to generate
> interfaces when variables are passed by address or value. Note how
> interfacing C and fortran using iso_c_binding is much simpler than generating
> the fortran bindings.
Actually I don't see that it is any simpler than our Fortran interfaces
(better, portable, but not simpler).
> How flexible is the code that generates fortran interfaces? Could it be
> easily hacked to use the iso_c_binding module?
It would be worth it to handle character strings which we now handle
manually. Maybe someday some ambitious person with time on their hands can
change it. I don't see a huge upside in changing it (some upside in not
needing to do character strings manually but that is all). With so much fun
stuff to do in (and new functionality to add to) PETSc I don't want time wasted
on something that doesn't make a big difference.
You don't have an example of passing an array of character strings from
Fortran to C. Is this because the standard doesn't provide a way?
Barry
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