[Python-Dev] Baffled by PyArg_ParseTupleAndKeywords modification (original) (raw)

"Martin v. Löwis" martin at v.loewis.de
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 PyArgParseTupleAndKeywords() 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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