[petsc-dev] meaning of PETSC_USE_EXTERN_CXX?

[Barry Smith]

On Mar 5, 2013, at 6:24 PM, Jed Brown <jedbrown at mcs.anl.gov> wrote:

> 
> On Tue, Mar 5, 2013 at 6:02 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:
>    We have --with-clanguage=c or c++   (this is already weird, most packages don't strife to be built either with C or C++)
>                   --with-c-support=0,1             (compile with C++ but with C bindings so C application can use it)
> 
>               User Code                PETSc compiled with
>           ------------------------          C                  C++
>                     C                           x                   x
>                     C++                       x                   x
> 
>             Hope back into Satish's way back machine and ask the question "why do we have this c-support business"? Seems like it complicates
> life a lot?
> 
> I would just unconditionally use extern "C" when compiling PETSc with a C++ compiler.

   Ok, and this will still support all four cases above. How do we do that? And would it simplify the mess we have now?

> We don't use overloading (PetscPolymorphic* was removed last spring) so I don't think there is any functional reason to mangle symbols. AFAICT, the only functional reason for building PETSc with a C++ compiler is to use C++ complex

   Yes, if a C++ programmer is using PETSc and complex numbers this is a legitimate case

> (and perhaps because the C++ compiler catches different errors than the C compiler).

  Yes, this is a legitimate use of our testing PETSc regularly with C++.

  Barry