[petsc-dev] need c++ expert help

[Smith, Barry F.]

 Jed

  I have merge https://bitbucket.org/petsc/petsc/commits/branch/jed/tests-cxx-linker into barry/more-to-new-test-harness on crank
using the /sandbox/petsc/petsc.next-2 with arch-linux-gcc-ifc-cmplx which is where the compile/link problem appeared. The error no longer appears and thus appears to compile/link the example correctly.

   There were some conflicts with the merge in examples I didn't bother to deal with in the test.

   So what to do? Do I do the merge of jed/tests-cxx-linker  into barry/more-to-new-test-harness properly and then merge into next and hope it breaks nothing on any machine tonight?

   Barry


   

> On Jan 1, 2018, at 1:13 PM, Jed Brown <jed at jedbrown.org> wrote:
> 
> 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?