From: Charles Mills <cmills@...>
Date: 2005-05-19T04:20:13+09:00
Subject: Re: howto make something like Errno::##, for my C ext, or do I need to?


Berger, Daniel wrote:
> > -----Original Message-----
> > From: Charles Mills [mailto:cmills@freeshell.org]
> > Sent: Wednesday, May 18, 2005 12:20 PM
> > To: ruby-talk ML
> > Subject: Re: howto make something like Errno::##, for my C
> > ext, or do I need to?
> >
> >
> >
> > Sam Roberts wrote:
> > > I'm wrapping a library, it returns its errors as numbers (many of
> > them,
> > > too many to wrap even automatically), and I don't know how to
raise
> > > exceptions.
> > >
> > > I've looked at how ruby deals with unix error numbers. I
> > guess I could
> > > cut-n-paste all the code to that my extension does the same...
> > but
> > > that seems wrong, somehow.
> > >
> > > What I'd really like to do is have only one error class, but
raise
> > > objects as exceptions, with the objects @errno set to the
> > value, I'd
> > > do this in ruby like this:
> > >
> > >   class MyErr < StandardError
> > >     attr_reader :eno
> > >     def initialize(eno); @eno = eno; end
> > >   end
> > >
> > >
> > >   ...
> > >     raise MyError.new(35)
> > >
> > > Looking at the exception raising APIs in README.EXT, I can't
quite
> > see
> > > how to do this.
> > >
> >
> > In short:
> > rb_exc_raise(my_err_new(eno));
> >
> > You probably want to have the ability to add a message to
> > your error objects so you may want to do:
> > rb_exc_raise(my_err_new("msg", eno));
> >
> > or define a function like
> >
> > static void
> > raise_my_err(int eno, const char *fmt, ...)
> > {
> >     va_list args;
> >     char buf[BUFSIZ];
> >
> >     va_init_list(args, fmt);
> >     vsnprintf(buf, BUFSIZ, fmt, args);
> >     va_end(args);
> >     rb_exc_raise(my_err_new(buf, eno));
> > }
> >
> > most of the above is a copy and paste from code in error.c.
> > I think your new function would look something like this:
> >
> > static VALUE
> > my_err_new(const char *buf, int eno)
> > {
> >   VALUE self = rb_exc_new2(cMyErr, buf);
> >   rb_iv_set(self, "@eno", INT2FIX(eno));
> >   return self;
> > }
> >
> > -Charlie
>
> Doesn't rb_sys_fail(0) work for this scenario?  I thought if a C
> function failed, you could call rb_sys_fail(0) and it would raise the
> appropriate Errno.  Or am I confused?
>
> Dan

Yeah that works too, if your using the standard library functions.  I
thought from the OP that the error numbers he was working with were not
related to those used by the std lib, but I may be wrong.

-Charlie