#define XXXType const char* ----> #define XXXType char* ?

[Lisandro Dalcin]

On 6/23/08, Barry Smith <bsmith at mcs.anl.gov> wrote:
>
>   Here is my problem: (happens all over the code)
>
>  argument of type "const char *" is incompatible with parameter of type
> "const VecType={char *}

So you ARE NOT using GCC, righ?

>  The problem seems to be that once I have created the new type (with
> typedef) the const now effects
>  the variable (not the array that the variable points to). const char *
> means I can change the variable (pointer)
>  but I cannot change the data it points to, which is what I want.

Well, I'm not a C lawyer, but such a behavior really surprises me.

Could you try instead this (note the inversion of type specifier
(char) and type qualifier (const)):

typedef char const* VecType;

I'm almost sure this is valid C++ (and completelly equivalent to the
former 'typedef const char* VecType'), but not so sure if it is valid
C89 or even C99.

With a bit of luck, your compiler will be happy with this. And with
more testing on other compilers (wich I do not have access to, sorry!)
perhaps that could be the way to go??


>
> > Barry, I do not understand what's going on with your compiler. Perhaps
> > my GCC is too old? (even when -Wwrite-strings is being passed ??)
> >
> > I've just changed the '#define' and used the 'typedef', and PETSc
> > compile (configure.py ... && make) just passed without any warning...
> > Furthermore, 'make test' 'make testexamples' also passed just fine.
> >
> > Perhaps my brain is not working well, but I do not see why all this is
> > an issue as long as the base PetscObject structure says 'char*
> > type_name'.
> >
> > You can always build on a 'char*' (note: non-const) buffer what you
> > want, and pass it to VecSetType(), or perhaps just replace 'type_name'
> > in internal PETSc code.
> >
> > IMHO, user-level PETSc interface should be simple, even if that iff
> > internally PETSc has to relax a bit the rules (ie. using a 'char*'
> > variable instead of a 'MatType' variable to build something like the
> > "seqsbaij" string from its pieces "seq", "s", "b", "aij").
> >
> > Am I missing something? What do you actually want to do with 'type_name'?
> >
> > On 6/23/08, Barry Smith <bsmith at mcs.anl.gov> wrote:
> >
> > >
> > > > Mmm, just a bit ugly you have to add the 'const' keyword. I insist:
> > > > What would be the problem with ... ??
> > > >
> > > > typedef const char* VecType;
> > > >
> > > >
> > >
> > >  Two problems.
> > >
> > >  The VecType is a const which means one cannot build them on the fly and
> > > copy into them etc
> > >
> > >  Second with the typedef one cannot do all the string manipulation on
> them.
> > > For example even the
> > > PetscStrcpy() in PetscHeaderCreate_Private() of type_name does not work.
> > >
> > >  It would be nice to use a typedef instead of a define to build it but
> it
> > > looks impossible. (Try it,
> > > just change one of them and try to compile PETSc, the screaming is
> > > relentless.)
> > >
> > >  Barry
> > >
> > >
> > > On Jun 23, 2008, at 2:38 PM, Lisandro Dalcin wrote:
> > >
> > >
> > >
> > > > On 6/23/08, Barry Smith <bsmith at mcs.anl.gov> wrote:
> > > >
> > > >
> > > > >
> > > > > A while ago I made XXType (MatType, VecType etc) const char*
> > > > >
> > > > >
> > > > >
> > > >
> > > > Well, you actually did
> > > >
> > > > #define VecType const char*
> > > >
> > > > instead of
> > > >
> > > > typedef const char* VecType;
> > > >
> > > > which IMHO is the right way.
> > > >
> > > >
> > > >
> > > > > I now think that was a mistake.
> > > > >
> > > > >
> > > >
> > > > Yep, the '#define' way can cause problems ;-)
> > > >
> > > >
> > > >
> > > >
> > > > > I'd like to change them to just  char*
> > > > >
> > > > >
> > > >
> > > > But why not the 'typedef' way ??
> > > >
> > > >
> > > >
> > > > > Can anyone suggest a technical reason why this is a bad idea before
> I
> > > > >
> > > >
> > > push
> > >
> > > >
> > > > > the code?
> > > > >
> > > > > Note this means if you have code like
> > > > >
> > > > > VecType t = VECMPI;
> > > > >
> > > > > you would need to change it to
> > > > >
> > > > > const VecType t = VECMPI;
> > > > >
> > > > >
> > > > >
> > > >
> > > >
> > > >
> > > > --
> > > > Lisandro Dalcín
> > > > ---------------
> > > > Centro Internacional de Métodos Computacionales en Ingeniería (CIMEC)
> > > > Instituto de Desarrollo Tecnológico para la Industria Química (INTEC)
> > > > Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET)
> > > > PTLC - Güemes 3450, (3000) Santa Fe, Argentina
> > > > Tel/Fax: +54-(0)342-451.1594
> > > >
> > > >
> > > >
> > >
> > >
> > >
> >
> >
> > --
> > Lisandro Dalcín
> > ---------------
> > Centro Internacional de Métodos Computacionales en Ingeniería (CIMEC)
> > Instituto de Desarrollo Tecnológico para la Industria Química (INTEC)
> > Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET)
> > PTLC - Güemes 3450, (3000) Santa Fe, Argentina
> > Tel/Fax: +54-(0)342-451.1594
> >
> >
>
>


-- 
Lisandro Dalcín
---------------
Centro Internacional de Métodos Computacionales en Ingeniería (CIMEC)
Instituto de Desarrollo Tecnológico para la Industria Química (INTEC)
Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET)
PTLC - Güemes 3450, (3000) Santa Fe, Argentina
Tel/Fax: +54-(0)342-451.1594