[petsc-users] Putting petsc in a namespace

[Jed Brown]

Florian Lindner <mailinglists at xgm.de> writes:

> Hello,
>
> This may be rather a C/C++ question, but ...
>
> I encapsulate some petsc functions into c++ classes. Since I don't want 
> to pull all petsc symbols into the global namespace for anyone using my 
> classes I try to put petsc into it's own namespace:
>
> Header petsc.h:

Note that there is already a petsc.h in the PETSc distribution.  It is
different from yours.

> namespace petsc {
> #include "petscmat.h"
> }
>
> class Vector {
>    petsc::Vec vector;
> }
>
>
> Implementation petsc.cpp:
>
> #include "petsc.h"
>
> namespace petsc {
> #include "petscviewer.h"
> }
>
> using namespace petsc;
>
>
> User:
>
> #include "petsc.h"
> #include <petscksp.h>  // if the user wants he can import parts of petsc 
> of course
>
>
> But this gives a massive amount of error messsages like:
>
> mpic++ -o petsc.o -c -O0 -g3 -Wall 
> -I/home/florian/software/petsc/include 
> -I/home/florian/software/petsc/arch-linux2-c-debug/include petsc.cpp
> mpic++ -o prbf.o -c -O0 -g3 -Wall -I/home/florian/software/petsc/include 
> -I/home/florian/software/petsc/arch-linux2-c-debug/include prbf.cpp
> In file included from 
> /home/florian/software/petsc/include/petscksp.h:6:0,
>                   from prbf.cpp:9:
> /home/florian/software/petsc/include/petscpc.h:9:14: error: 
> 'PetscErrorCode' does not name a type
>   PETSC_EXTERN PetscErrorCode PCInitializePackage(void);

What do you expect when you put some things in the namespace and include
dependencies outside the namespace?

namespaces don't play well with macros (including header guards).  I
don't think what you are attempting is a good use of time, but if you do
it, I would recommend creating a public interface that does not include
any PETSc headers, thus completely hiding the PETSc interface.
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