On Wed, Mar 16, 2016 at 11:28:30AM +0100, Harald Welte wrote: Yes, Holger has applied the patch with exactly that change. Yet this has me confused. A while back I concluded that C doesn't allow passing non-const instances to functions that expect a const arg. That was discussed on this list in January: http://lists.osmocom.org/pipermail/openbsc/2016-January/001051.html http://lists.osmocom.org/pipermail/openbsc/2016-January/001055.html How is this different from the conclusion that Jacob confirmed two months ago? Is it int (primitives) vs. struct?? Thanks! ~Neels

On Thu, Mar 17, 2016 at 08:06:32AM +0100, Harald Welte wrote: I'm very familiar with that and want to use this everywhere and always, which is why my conclusion that it apparently didn't work was quite a disappointment. Glad to see that it does work after all... What bugs me is that I don't understand the apparent corner case where it doesn't work. First, let's clarify: const int * const x; the pointer x can't be modified, neither can the int at *x be modified. const int *x; pointer x can be modified, but the int at *x can't be modified. const int **x; x can be modified, *x can be modified, but the int at **x can't be modified. right? Let's look at a simple example that works without warning: I only want to modify a pointer, not the ints. const int *func(const int *yy) { return yy + 1; } int main(void) { int y[2] = {23, 42}; int *yy = y; return *func(yy); // returns 42 } This works perfectly. I pass a pointer to a mutable int, though the function expects a pointer to a const int. No compiler warning. And the failing example again; it does the exact same thing, only it returns the modified pointer in an output-argument, using a pointer to a pointer to a const int: void func(const int **yyy) { (*yyy) ++; } int main(void) { int y[2] = {23, 42}; int *yy = y; func(&yy); return *yy; // returns 42 } And here I get the warning: cc check.c -o check check.c: In function ‘main’: check.c:11:14: warning: passing argument 1 of ‘func’ from incompatible pointer type func(yyy); ^ check.c:1:6: note: expected ‘const int **’ but argument is of type ‘int **’ void func(const int **yyy) ^ I'm quite happy that it seems to be only a corner case, and I'll be consting aggressively and happily ever after :) Yet it's a stupid corner case. Would be great if someone had an explanation to this odd gcc behavior. Maybe it's rather a question for another mailing list, too... ~Neels -- - Neels Hofmeyr <nhofmeyr(a)sysmocom.de> http://www.sysmocom.de/ ======================================================================= * sysmocom - systems for mobile communications GmbH * Alt-Moabit 93 * 10559 Berlin, Germany * Sitz / Registered office: Berlin, HRB 134158 B * Geschäftsführer / Managing Directors: Holger Freyther, Harald Welte

On Thu, Mar 17, 2016 at 04:25:48PM +0100, Harald Welte wrote: Heh, good answer :) At least I know now that it's a corner case. ~Neels