On Wed, Aug 19, 2009 at 10:34 AM, Joerg Schilling < Joerg.Schilling at fokus.fraunhofer.de> wrote:
> Vincent Torri <vincent.torri at gmail.com> wrote: > > > with a code similar to that one: > > > > int i = 2; > > int j = 2; > > void *a = &i; > > void *b = &j; > > unsigned long delta = a - b; > > > > the compiler is displaying the warning "pointer to void or function used > in > > arithmetic". Why is it doing so whe computing an offset ? I know that > adding > > or substracting an offset to a void pointer is illegal, but when > calculating > > an offset, using typed or void pointers is exactly the same. > > A "void" is an "object" of unknown/unspecified size. > > Pointer arithmetics for: > > delta = a - b; > > - means a and b need to be objects of the same type > > - the differentce between the numerical values in a and > b is computed > > - the result is divided by sizeof (a) > > Did you ever try to use sizeof (void) in your code? > > How do you like to divide by an unknown number? > > A correct C-compiler does not print a warning but an error message and > aborts compilation. What the sun compiler currently does is a courtesy > to GCC users as GCC treats sizeof (void) == 1 which is in conflict with > the C-standard. If the Sun compiler would work correctly and abort here, > a lot of (broken) OSS software could not be compiled. > hoo, right ! i've forgotten that it divides by the size of variables (and it can be negative too) thank you to both of you ! Vincent Torri -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://mail.opensolaris.org/pipermail/tools-compilers/attachments/20090819/ca69ec19/attachment.html>
