Re: struct syntax

[Owen Taylor <otaylor redhat com>]

Federico Mena Quintero <federico ximian com> writes:

> On 01 Jul 2001 11:32:50 -0400, Nathan Cullen wrote:
> > 
> > In Gtk+/GNOME programming I often see: 
> > 
> > /* Style 1 */
> > typedef struct _Thing Thing;
> > struct _Thing {
> > 	/* stuff */
> > };
> > 
> > I also see:
> > 
> > /* Style 2 */
> > typedef struct {
> > 	/* stuff */
> > } Thing;
> > 
> > 
> > It seems as if Style 2 is alot clearer, and gets rid of an unnecessary
> > middleman.
> > 
> > The only application of Style 1 that I can concieve of is so that you
> > could hide implementation details from clients by placing the typedef in
> > the header and defining the struct in the corresponding .c file.
> > clients.  I saw this used effectively in bonobo-ui-node.
> > 
> > So why do I see Style 1 all over the place?  There must be something I'm
> > missing.
> Historical reasons; the original GTK+ had Style 1 all over the place and
> it stuck.
> 
> Style 1 is of course ugly and evil, and all Right Minded people should
> use Style 2 :)

You frequently want forward declarations because:

 A) Your structures are opaque to user code [ a "good thing" ]

 B) Your structures reference each other recursively, or
    reference themselves.

 C) You simply don't want to have to worry about ordering.

So, we've always found it easier and more logical to _always_
forward declare, rather than forward declare a random 
subset.

If you consistently name the structure and the typedef,
then it doesn't make it any harder to read the code ...
you always know that the structure for GtkFoo is called
struct _GtkFoo.

(People frequently point out that the underscore is unnecessary
and technically invalid. We know that, we aren't going
to change at this point, and if a C library calls things
_Gtk... then we'll suffer the conquences.)

Many "utility" structures used right at the point of
declaration within a single C file are, however, done
without the forward declaration.  

Regards,
                                        Owen