> > > Included is a manpage documenting the offsetof() macro; please
> > > consider including it.
> >
> > Excellent idea! Thanks for the page. It will go in 2.34.
> It was my idea .. I guess I found it in undocumented.3.
Yep -- I removed it from undocumented.3 already.
[...]
> > > printf("%d\n", offsetof(struct a, c));
> > > exit(EXIT_SUCCESS);
> > > }
> > > .fi
> > > .SH NOTES
> > > \fBoffsetof\fP can be implemented as:
> > > .sp
> > > .nf
> > > \fB#define offsetof(\fItype\fP, \fPmember\fP) \\
> > > \fB&((type *)0)->\fImember\fP - (char *)((\fPtype\fP *)0)
> > > .fi
> >
> > I'm inclined to leave the above out (it could vary on some systems).
> > But anyway, why do you write the above when glibc says:
> >
> > #define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)
> Actually, I have:
>
> #define offsetof(TYPE, MEMBER) __builtin_offsetof (TYPE, MEMBER)
>
> And in gcc-3.4 it is even uglier:
>
> /* The cast to "char &" below avoids problems with user-defined
> "operator &", which can appear in a POD type. */
> #define offsetof(TYPE, MEMBER) \
> (__offsetof__ (reinterpret_cast <size_t> \
> (&reinterpret_cast <const volatile char &> \
> (static_cast<TYPE *> (0)->MEMBER))))
>
> But I don't know why it would be necessary to subtract the casted zero
> :) At one point I had quite an amusing conversation about this.
Okay -- I will remove this definition from the man page,
> I wrote it myself so I wasn't copying libc (although my source was gcc
> anyway) and to make sure I still understood it. Do you have a glibc
> source, too?
There are many glibc sources (different versions) -- I
have the source of a large number of them.
Cheers,
Michael
--
Michael Kerrisk
maintainer of Linux man pages Sections 2, 3, 4, 5, and 7
Want to help with man page maintenance?
Grab the latest tarball at
ftp://ftp.win.tue.nl/pub/linux-local/manpages/,
read the HOWTOHELP file and grep the source
files for 'FIXME'.
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