What is the expected behavior of attribute nonnull for C++

[Steven Bosscher]

On 4/28/06, Mark Mitchell <mark@codesourcery.com> wrote:
> Steven Bosscher wrote:
>
> > The documentation of the nonnull attribute says:
> >
> > `nonnull (ARG-INDEX, ...)'
> >      The `nonnull' attribute specifies that some function parameters
> >      should be non-null pointers.  For instance, the declaration:
> >
> >           extern void *
> >           my_memcpy (void *dest, const void *src, size_t len)
> >                 __attribute__((nonnull (1, 2)));
> >
> >      causes the compiler to check that, in calls to `my_memcpy',
> >      arguments DEST and SRC are non-null.
> >
> >
> > So do we expect our users to know that they should add 1 to every
> > ARG-INDEX they pass?  That would make this a documentation bug.  Or
> > is this a "real" bug in G++, and should the compiler correct the
> > ARG-INDEX numbers so that the middle-end doesn't get confused?
>
> I think this is a documentation bug.

OK.  Andrew Pinski already pointed out http://gcc.gnu.org/PR1607 as
another example.

> (Well, really, I think it's a design bug; the attribute should be
> applied to the parameters, rather than to the entire function type, so
> that users didn't have to count.  In other words, it should be:
>
>   void f(__attribute((nonnull)) int *);
>
> But, that's just me being wishful.)

:-)

> The reason I think this is a documentation bug is that (a) it's always
> been this way, ergo we'd be breaking backwards compatibility to change
> it,

OK, Richard G. also mentioned this.  I'll prepare a documentation patch.

> and (b) some of these kinds of attributes could usefully apply to
> the "this" pointer.

That is why I was looking at this. We have http://gcc.gnu.org/PR27336,
and part of the fix could be to make the 'this' pointer always
non-NULL.  So far I haven't found anyone who can think of a situation
where 'this' can be NULL...

Thanks,

Gr.
Steven