On 18 févr. 2011, at 15:12, Philip Graham Willoughby wrote: > Adding casts to get rid of warnings is usually the wrong answer in my > experience. Certainly you should never cast the return value of a function > call because that hides the problems you get when it's implicitly returning > int because a required header is missing. I used to see a lot of C code > (usually from Windows programmers - does MSVC encourage this?) which has > stuff like this all over the place: > > struct something *fred = (struct something *)malloc(sizeof(struct > something)); > > Casting the return from malloc is never necessary - void * is assignable to > any non-function pointer type by definition. > > It becomes an extremely bad idea when you're building on a platform with > 64-bit pointers and a 32-bit int (such as everything I use) and you have the > optimiser turned on – in this case if <stdlib.h> isn't included none of your > allocations will work properly and your program will crash. > > Best Regards, > > Phil Willoughby > --
My pure C must be rusted. Could you please elaborate why this line breaks with 64-bit pointers and 32-bit ints? fred is a 64 bit pointer of type struct something * malloc returns a 64 bit pointer of type void * casting that pointer to struct something * makes it a 64-bit pointer of type struct something *, which is then assigned to fred. I can't see how 64-bitness of pointers can hurt. Similarly, malloc takes one argument of type size_t. On such a platform size_t is probably defined as long (or long long), but that is irrelevant, because the sizeof intrinsic is defined as returning a size_t as well. Now even if size_t is defined as int, this would only have an impact for structs larger than 2^31 bytes, which are few are far between, and that impact would be unrelated to the typecast. I can't see how 32-bitness of ints can hurt. What did I miss? JD _______________________________________________ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
