Erik Trulsson <[EMAIL PROTECTED]> writes:
> On Tue, Jul 12, 2005 at 03:08:54PM -0700, Joe Buck wrote:
>> On Tue, Jul 12, 2005 at 11:42:23PM +0200, Erik Trulsson wrote:
>> > Pointer subtraction is only well defined if both pointers point to elements
>> > in the same array (or one past the end of the array). Otherwise the
>> > behaviour is undefined.
>>
>> While this is correct, there are certain cases that the standard leaves
>> undefined but that nevertheless can be useful; for example, pointer
>> subtraction can be used to estimate the amount of stack in use (of
>> course, it is necessary to know if the stack grows upward or downward).
>>
>> Similarly, in an OS kernel, comparing pointers may make sense.
>
> Yes, there are some situations where it can be useful to compare pointers
> to different objects, but then you need to make sure that the compiler you
> use actually supports that.
>
> I believe most C compilers support it in practice, but few, if any, have
> actually documented it as a supported extension to C.
I don't think we should, either. People who want to do this can just
cast both pointers to size_t.
--
Falk
