[Python-Dev] Baffled by PyArg_ParseTupleAndKeywords modification

Fri Feb 10 18:02:03 CET 2006

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