[Python-Dev] Baffled by PyArg_ParseTupleAndKeywords modification

[Jeremy Hylton]

On 2/10/06, Jeremy Hylton <jeremy at alum.mit.edu> wrote:
> It looks like a solution may be to define it as "const char * const *"
> rather than "const char **".  I'll see if that works.

No.  It doesn't work.  I'm not sure about this one either, but some
searching suggests that you can pass a char** to a function taking
const char* const* in C++ but not in C.  Sigh.  I don't see any way to
avoid a warning in Jack's case.

Jeremy

>
> 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
> >
>