Re: [gtk-list] Re: How to use a gpointer?

[Tim Janik <timj gtk org>]

On Thu, 4 Mar 1999, Ulric Eriksson wrote:

> 
> On Thu, 4 Mar 1999, Tim Janik wrote:
> 
> > after having seen various statements on this topic,
> > i think it's time to clarify some points.
> > 
> > for GLib to compile on several different platforms, certain
> > assumptions can be made about its data types.
> > 
> > gint8    sizeof (gint8) = 1 byte, signed
> > guint8   sizeof (guint8) = 1 byte, unsigned
> > gint16   sizeof (gint16) = 2 bytes, signed
> > guint16  sizeof (guint16) = 2 bytes, unsigned
> > gint32   sizeof (gint32) = 4 bytes, signed
> > guint32  sizeof (guint32) = 4 bytes, unsigned
> > gint     is merely an alias for the system's int and guarranteed
> >          to be >= 4 bytes in size, signed.
> > guint	 is and unsigned gint.
> > glong	 is an alias for the system's long and guarranteed to be >=
> >          sizeof (gint), signed.
> > gulong	 is an unsigned glong.
> > gpointer is essentially a void* and guarranteed to be >= sizeof (gint)
> >          and <= sizeof (glong) in size.
> 
> Well spank me with a wet noodle if I'm wrong, but here is cut-and-paste
> from glib.h of 1.2:
> 
> 8<--------
> typedef int    gint;
> ...
> typedef void* gpointer;
> 8<--------
> 
> There is nothing in these typedefs that guarantees that a gint will fit
> in a gpointer.
> 
> Some of the headers are generated when Glib is compiled, but not glib.h,
> so I suppose that the above is the same on the Alpha.

yes, and on the alpha sizeof(gpointer)=8, sizeof(gint)=4 and sizeof(glong)=8,
so an int can be stored in a pointer without lossage and a pointer can be
stored in a long without lossage, so my above summary still holds.
in fact, we haven't yet encountered a 32bit system (or 64bit system for that
matter) where sizeof(gpointer) would be less than 4, and i guess we never
will, so that pretty much makes up the above guarrantee.
the fact that some typedefs are not special cased in glibconfig.h doesn't mean
that one couldn't make assumptions about them ;)

> 
> Ulric
> 

---
ciaoTJ