Date: Sat, 26 Feb 2000 00:11:22 -0500 From: "Crist J. Clark" <cjc@cc942873-a.ewndsr1.nj.home.com> To: Marco Molteni <molter@csl.sri.com> Cc: freebsd-chat@FreeBSD.ORG Subject: Re: how to do this C preprocessor trick? Message-ID: <20000226001121.A20702@cc942873-a.ewndsr1.nj.home.com> In-Reply-To: <20000225182432.A5017@sofia.csl.sri.com>; from molter@csl.sri.com on Fri, Feb 25, 2000 at 06:24:32PM -0800 References: <20000225182432.A5017@sofia.csl.sri.com>
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On Fri, Feb 25, 2000 at 06:24:32PM -0800, Marco Molteni wrote:
> Hi all,
>
> I have a function that takes a variable number of arguments:
>
> void d_printf(const char *format, ...)
>
> I would like to make it print automatically the function name
> from which it is called, eg instead of doing
>
> f() { d_printf("f: blabla", x, y, z); }
>
> doing simply
>
> f() { d_printf("blabla", x, y, z); }
>
> To do that, I though of wrapping d_printf() around a macro like
>
> #define dprintf(x) d_printf(__FUNCTION__, x)
>
> but whatever combination I use (also with #), the thing is not going to work:
>
> main.c:231: macro `d_printf' used with too many (4) args
>
> Is it possible to trick the C preprocessor to do what I want?
Yeah, I use the same type of thing to produce error messages. I'm
having a little bit of trouble understanding exactly what you are
trying to do above, so I'll just show my solution to my problem.
I wanted to just be able to do,
errmsg(char fmt, ...)
But have it print,
cmd(file:line)- Error message
Where 'cmd' is the name of the program (the tail of argv[0]), 'file'
is the C source file name, and 'num' is the line number.
char *cmd
void _errmsg(char *fmt, ... )
{
va_list ap;
va_start(ap,fmt);
vfprintf(stderr,fmt,ap);
va_end(ap);
}
#define errmsg fprintf(stderr,"%s(%s:%d)- ",cmd,__FILE__,__LINE__); _errmsg
Gets me around the varargs in the precompiler by not using _any_
args in the macro. So,
errmsg("cannot fine file: %s\n",str);
Expands to,
fprintf(stderr,"%s(%s:%d)- ",cmd,__FILE__,__LINE__); _errmsg("cannot fine file: %s\n",str);
And you know, it works. Big help in debugging big apps. When it's sent
bound for users, I make the messages a bit less verbose, but only
takes the one change.
--
Crist J. Clark cjclark@home.com
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