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

[Barry Smith]

   Here is my problem: (happens all over the code)

argument of type "const char *" is incompatible with parameter of type  
"const VecType={char *}

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.

    Barry


On Jun 23, 2008, at 3:51 PM, Lisandro Dalcin wrote:

> 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
>