[petsc-dev] need c++ expert help

[Matthew Knepley]

On Sun, Dec 31, 2017 at 3:14 PM, Jed Brown <jed at jedbrown.org> wrote:

> Matthew Knepley <knepley at gmail.com> writes:
>
> > On Sun, Dec 31, 2017 at 2:35 PM, Jed Brown <jed at jedbrown.org> wrote:
> >
> >> Matthew Knepley <knepley at gmail.com> writes:
> >>
> >> > On Sun, Dec 31, 2017 at 1:55 PM, Jed Brown <jed at jedbrown.org> wrote:
> >> >
> >> >> These look like linker errors and that build uses
> >> >> --with-cxxlib-autodetect=0.  We either need a rule to *link* C++
> using
> >> >> CXX (i.e., mpicxx) or add LIBS=-lstdc++.
> >> >>
> >> >
> >> > I thought we were doing this (linking C++ mains with CXX).
> >>
> >> After compiling to the object file (ex3.o) we don't know what language
> >> main was written in, and this doesn't solve the actual problem that C++
> >> linking is required if any object (not just main) depends on C++.
> >>
> >
> > My thinking here was the following:
> >
> >   1) No C++ is allowed in PETSc, unless --with-clanguage=cxx, in which
> case
> > the linker is C++
> >   2) If C++ is in an external library, then that configure requires the
> C++
> > library
> >   3) The executable itself could be C++, in which case I proposed using
> the
> > C++ linker explicitly
> >
> > About not knowing which objects come with C++ main: I thought we did.
> Don't
> > they go into a separate set?
>
> Right, we do have that information for tests.  Note that a single test
> executable can depend on multiple source files, and the one containing
> main might not be C++ while another is.  I don't know if there are any
> such instances in PETSc.
>

True. I think we just have to have a policy against that.


> I can change the build rules for tests with C++ sources later today.
>

Cool.

  Thanks,

    Matt

-- 
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

https://www.cse.buffalo.edu/~knepley/ <http://www.caam.rice.edu/~mk51/>
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