Re: Initializer and initialization macros in queue.h

[Joerg Sonnenberger <joerg%britannica.bec.de@localhost>]

On Sat, Sep 12, 2015 at 02:23:38PM +0200, Matthias-Christian Ott wrote:
> On 2015-08-09 14:26, Joerg Sonnenberger wrote:
> > On Fri, Jul 31, 2015 at 10:25:32AM +0000, Matthias-Christian Ott wrote:
> >> queue.h defines initializers macros (e.g. LIST_HEAD_INITIALIZER) and
> >> initialization macros (e.g. LIST_INIT). The initializer macros have been
> >> introduced in NetBSD. I'm not sure how what's the intended purpose of
> >> both macro types.
> > 
> > The head initializer macros allow the globals to be usable directly
> > without any runtime initialisation. That can simplify setup logic a lot.
> 
> So in the following code head1 and head2 would initialized to the same
> value?
> 
> #include <stddef.h>
> #include <sys/queue.h>
> 
> struct entry {
>     LIST_ENTRY(entry) link;
> };
> 
> LIST_HEAD(head, entry);
> 
> struct head head1 = LIST_HEAD_INITIALIZER(&head1);
> 
> int main(void)
> {
>     struct head head2;
> 
>     LIST_INIT(&head2);
> 
>     return 0;
> }

Well, they would of course have different values, but both are
initialised. This is equivalent to your second example, assuming nothing
runs before main.

Joerg