On Sun, Aug 04, 2024 at 08:02:25PM GMT, Martin Uecker wrote: > Hi Alex, Hi Martin,
> > Is this missing diagnostics? > > > > $ cat star.c > > void foo(char (*a)[3][*], int (*x)[__lengthof__(*a)]); > > void bar(char (*a)[*][3], int (*x)[__lengthof__(*a)]); > > void foos(char (*a)[3][*], int (*x)[sizeof(*a)]); > > void bars(char (*a)[*][3], int (*x)[sizeof(*a)]); > > > > int > > main(void) > > { > > int i3[3]; > > int i5[5]; > > char c35[3][5]; > > char c53[5][3]; > > > > foo(&c35, &i3); > > foo(&c35, &i5); // I'd expect this to fail > > Yes, this should fail. The int (*)[5] is not > compatible with int(*)[3]. > > > bar(&c53, &i3); // I'd expect this to fail > > This is no contraint violation, because int (*)[5] is > compatible with int (*i)[*], so this needs to be accepted. No constraint, but I'd expect a diagnostic from -Wextra (array-bounds?). > It is then UB at run-time and the patches I posted recently Can you please send a link to those patches? > would catch this. When possible, a compile time warning > would be nice and I am also looking into this. > > It would also be good if we could allow a compiler to > reject this at compile time... also something I am > thinking about. Thanks! > > > bar(&c53, &i5); > > > > foos(&c35, &i3); > > foos(&c35, &i5); // I'd expect this to fail > > bars(&c53, &i3); // I'd expect this to fail > > These are both okay, because the sizeof is not an integer > constant expressions (both int[*][3] and int[3][*] have > variable size), so the last argument has to be compatible > with int[*] which they both are. Both would trigger > run-time UB then because the size is then 15. D'oh! I screwed it. I wanted to have written this: $ cat star.c void foo(char (*a)[3][*], int (*x)[__lengthof__(*a)]); void bar(char (*a)[*][3], int (*x)[__lengthof__(*a)]); void foo2(char (*a)[3][*], int (*x)[sizeof(**a)]); void bar2(char (*a)[*][3], int (*x)[sizeof(**a)]); int main(void) { int i3[3]; int i5[5]; char c35[3][5]; char c53[5][3]; foo(&c35, &i3); foo(&c35, &i5); // I'd expect this to err bar(&c53, &i3); // I'd expect this to warn bar(&c53, &i5); foo2(&c35, &i3); // I'd expect this to warn foo2(&c35, &i5); bar2(&c53, &i3); //bar2(&c53, &i5); // error: -Wincompatible-pointer-types } $ /opt/local/gnu/gcc/lengthof/bin/gcc -Wall -Wextra star.c -S $ > > Martin Cheers, Alex -- <https://www.alejandro-colomar.es/>
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