Re: Help requested with P99-based macro to create Wayland listeners

On 10/04/2024 18:08, Tim Rentsch wrote:

Ben Bacarisse <ben.usenet@bsb.me.uk> writes:
 

David Brown <david.brown@hesbynett.no> writes:
>

On 09/04/2024 22:20, Blue-Maned_Hawk wrote:
>

David Brown wrote:
>

On 09/04/2024 20:17, Blue-Maned_Hawk wrote:
>

Tim Rentsch wrote:
>

What is it that you want to accomplish?

>
As i stated in the subject line, i am trying to create a macro to
create Wayland listeners.

>
Assume, for the sake of argument, that no one knows or cares anything
about Wayland or listeners.

>
<https://xkcd.com/1432/>
>

You are trying to use a set macros to expand to some code.  Start by
showing what code you want to get from examples of using your macros -
then people can try to help get the macros right.

>
MAKE_LISTENER(wl_registry, global, global_remove);
?
static const struct wl_registry_listener wl_registry_listener = { .global
= callback_wl_registry_global, .global_remove =
callback_wl_registry_global_remove };

>
#define _get_6th_arg(_1, _2, _3, _4, _5, _arg, ...) _arg
#define _fe_0(_global, _call, ...)
#define _fe_1(_global, _call, x) _call(_global, x)
#define _fe_2(_global, _call, x, ...) _call(_global, x) _fe_1(_global,
  _call, __VA_ARGS__)
#define _fe_3(_global, _call, x, ...) _call(_global, x) _fe_2(_global,
  _call, __VA_ARGS__)
#define _fe_4(_global, _call, x, ...) _call(_global, x) _fe_3(_global,
  _call, __VA_ARGS__)
#define expand_macro_for_each(_global, _macro, ...) \
     _get_6th_arg("ignored", __VA_ARGS__, \
     _fe_4, _fe_3, _fe_2, _fe_1, _fe_0)(_global, _macro, __VA_ARGS__)
>
>
#define MAKE_LISTENER(object_type, ...) _make_listener(object_type,
  __VA_ARGS__)
#define _listener_entry(_global, _field) , . _field = callback_ ## _global
## _ ## field

>
s/field/_field/

Correct - sorry about the typo.

 The bigger problem is that the proposed solution doesn't work
for more than five fields. 

I have no idea how many fields the OP might want, in order to judge if that is a big problem or not.  But I believe he'll be able to figure out how to extend it as necessary.

Clearly the idea is to define a
macro that works for an unlimited number of fields, or at least
a fairly large number.

If you have a way to extend it to unlimited numbers of fields, I would love to know - as far as I am aware, the lack of recursion or loops in the C pre-processor means that you always have to be limited like this. It is, I think, possible to make sequence of macros like this that split lists in half, so that you only need O(log N) submacros in order to support up to N arguments.  That would let you get to the level of very large numbers pretty quickly.