[petsc-dev] need c++ expert help

[Jed Brown]

Jed Brown <jed at jedbrown.org> writes:

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

The Python is just damn convoluted, but I was able to implement this by
deleting code.

https://bitbucket.org/petsc/petsc/commits/branch/jed/tests-cxx-linker

Barry, can you try this in whatever branch is giving you issues?