From: "Tim 'Zastai' Van Holder" <zastai AT hotmail DOT com>
Newsgroups: comp.os.msdos.djgpp
References: <200009011041 DOT MAA65728 AT login-2 DOT eunet DOT no>
Subject: Re: __attribute__ for pointers
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"Gisle Vanem" <gvanem AT eunet DOT no> wrote in message
news:200009011041 DOT MAA65728 AT login-2 DOT eunet DOT no...
> From: "Eli Zaretskii" <eliz AT is DOT elta DOT co DOT il> said:
>
> > > Date: Fri, 1 Sep 2000 08:00:44 +0200 (MET DST)
> > > From: Gisle Vanem <giva AT bgnett DOT no>
> > >
> > > extern int (*__printf) (const char *fmt, ...)
> > > #ifdef __GNUC__
> > >   __attribute__((format(printf,1,2)))
> > > #endif
> > > ;
> > >
> > > Where '__printf' points to either a stdio or a conio-type function.
> > >
> > > But gcc 2.95.2 doesn't seem to allow such '__attribute__' for a
pointer;
> > >
> > >  "argument format specified for non-function `__printf'"
> >
> > Did you try to put __attribute__ inside the parens in (*__printf)?
>
> Tried it, but doesn't work;
>
>   extern int (*__printf __attribute__((format(printf,1,2))))
>               (const char *fmt, ...);
> or
>   extern int (*__printf) __attribute__((format(printf,1,2)))
>               (const char *fmt, ...);
>
>
> > If that doesn't help either, try using a typedef.
>
> Did work either:
>
>   typedef int (*PrintFunc) (const char *fmt, ...);
>
>   extern PrintFunc __printf __attribute__((format(printf,1,2)));
>
> or
>   typedef int (*PrintFunc) (const char *fmt, ...)
>     __attribute__((format(printf,1,2)));
>
>   extern PrintFunc __printf;

I replied to your original post, but it seems that posts I make from work
rarely make it onto the NG (looks like I'll have to use Deja there then).

Basically you're indeed out of luck - the format attribute is only for
functions, not for variables (like your __printf) or types.

Because of the ..., you can't use a wrapper function to work around your
problem, but changing the systems slightly may help (of course, this may
not be possible, depending on where the possible values of __printf
come from).

First off, use this:
extern int (*__printf_func) (const char *fmt, va_list args);

Then, the following function can provide a format-checked wrapper:
extern int __printf (const char *fmt, ...)
#ifdef __GNUC__
   __attribute__((format(printf,1,2)))
#endif
;

This function is fairly straightforward:
int
__printf (const char *fmt, ...)
{
va_list args;
int retval;
  if (__printf_func == NULL)
    return 0; /* or perhaps -1? */
  va_start (args, fmt);
  retval = (*__printf_func)(fmt, args);
  va_end (args);
  return retval;
}

HTH,
Tim Van Holder

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