dolfin team mailing list archive

["Matthew Knepley" <knepley@xxxxxxxxx>]

On Sun, Mar 16, 2008 at 5:18 PM, Åsmund Ødegård <aasmund@xxxxxxxxx> wrote:
> On Sun, Mar 16, 2008 at 10:44 PM, Matthew Knepley <knepley@xxxxxxxxx> wrote:
>  > >  This is the behavior I observed, although it was more than a year ago
>  >  >  that I put a line in my makefile to determine if mpicxx existed in the
>  >  >  same path, and if not, try to use the mpicc (provided by PCC_LINKER) as
>  >  >  a C++ compiler.  I generally use openmpi, but often build PETSc
>  >  >  with-clanguage=C since I don't use the C++ interface (I'm playing with
>  >  >  sieve now so this has changed).  Then PCC_LINKER would give me a C
>  >  >  compiler (mpicc) and I would look for a C++ compiler at the same path
>  >  >  (since the code I was compiling was C++).  This worked great for me, but
>  >  >  it broke for some people who had PETSc install mpich2.  The problem was
>  >  >  that mpicc was actually a C++ compiler and there was no mpicxx at that
>  >  >  path.  It would have been a PETSc configured with-clanguage=C++.  In
>  >  >  trying to reproduce this with a recent PETSc (2.3.3-p6 and petsc-dev) it
>  >  >  looks like mpich2 produces just mpicc (which is not a C++ compiler) when
>  >  >  configured with-clanguage=C and correctly produces mpicxx when
>  >  >  with-clanguage=C++.  This is entirely sane behavior.  I'm not sure why
>  >  >  Osman is seeing the former behavior even with a recent PETSc.
>  >
>  >  Yes, if C++ is not turned on in PETSc, we will not generate an mpicxx when
>  >  installing MPICH2. For the C compiler, we take whatever is specified
>  >  using --with-cc
>  >  or the one we find by default if nothing is specified. You can see which one we
>  >  found using mpicc --show.
>  >
>
>  This make kind of sense, of course. But it also makes it a bit hard,
>  as Petsc tend to be quite picky about compilers. Dolfin is C++, so
>  some mpicxx is needed when Dolfin and Petsc are linked together. Maybe
>  the best solution is to skip the wrappers altogether, just extract
>  what we need from mpicc -show, and build the correct commands.

I really really would not do this. It will cause future pain. I used to do that
and gave up. The right thing to do is to actually ask for what you wany,
--with-clanguage=c++ when building PETSc since you do in fact need C++.
Then everything will work fine.

   Matt

>  Probably have to sleep on this :)
>
>  Åsmund
-- 
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