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[Python-Dev] Baffled by PyArg_ParseTupleAndKeywords modification

Jeremy Hylton jeremy at alum.mit.edu
Fri Feb 10 18:06:21 CET 2006 
It looks like a solution may be to define it as "const char * const *"
rather than "const char **".  I'll see if that works.

Jeremy

On 2/10/06, "Martin v. Löwis" <martin at v.loewis.de> wrote:
> Jeremy Hylton wrote:
> > I admit that I'm also puzzled by Jack's specific question.  I don't
> > understand why an array passed to PyArg_ParseTupleAndKeywords() would
> > need to be declared as const.  I observed the problem in my initial
> > changes but didn't think very hard about the cause of the problem.
> > Perhaps someone with better C/C++ standards chops can explain.
>
> Please take a look at this code:
>
> void foo(const char** x, const char*s)
> {
>         x[0] = s;
> }
>
> void bar()
> {
>         char *kwds[] = {0};
>         const char *s = "Text";
>         foo(kwds, s);
>         kwds[0][0] = 't';
> }
>
> If it was correct, you would be able to modify the const char
> array in the string literal, without any compiler errors. The
> assignment
>
>   x[0] = s;
>
> is kosher, because you are putting a const char* into a
> const char* array, and the assigment
>
>      kwds[0][0] = 't';
>
> is ok, because you are modifying a char array. So the place
> where it has to fail is the passing of the pointer-pointer.
>
> Regards,
> Martin
>
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