[petsc-dev] need c++ expert help

[Jed Brown]

"Smith, Barry F." <bsmith at mcs.anl.gov> writes:

>> On Dec 31, 2017, at 2:14 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.
>> 
>> I can change the build rules for tests with C++ sources later today.
>
>    Jed, are you indicating that you will resolve the original problem I reported? Where will you resolve it? The problem may come up in one of my branches.

I was going to put it in a new branch from 'master'.  There is
disgusting duplication in 'maint' that has since been fixed so I'd
rather not do it there.

Under what conditions is PCC_LINKER different from CC (or CXX when
clanguage=C++)?  I need to find a C++ linker and would prefer to use
$(CXX) rather than adding a new configure test.  I feel like the
generated petscvariables has an inordinate amount of duplication all
with non-standard names and no documentation.

The cheap way to fix your issue is to add LIBS=-lstdc++ to your
configure.