From:	"John M. Aldrich" <fighteer AT cs DOT com>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: Syntax Questions...
Date:	Mon, 01 Dec 1997 00:23:43 +0000
Organization:	Two pounds of chaos and a pinch of salt
Lines:	77
Message-ID:	<3482038F.4E54@cs.com>
References:	<3480E777 DOT 691C AT mailexcite DOT com>
Reply-To:	fighteer AT cs DOT com
NNTP-Posting-Host:	ppp205.cs.com
Mime-Version:	1.0
To:	djgpp AT delorie DOT com
DJ-Gateway:	from newsgroup comp.os.msdos.djgpp

BlueShade wrote:
> 
> First, I was wondering if anyone could tell me how to access "ellipses
> variables".  An example of what I'm babbling about is as follows.  If I
> define a function:
> 
>         void something( int x, int y, ... );
> 
> How do I access the variables that come in the ...?  Well, that's all
> for now...

Ah, the famous ellipsis.  You can access the variables represented by
the '...' using a special set of macros called va_args, and a special
set of display functions designed to handle them.  For example, here's a
small wrapper for printf() that echoes its output to a file:

#include <stdio.h>
#include <stdarg.h>

int my_printf( FILE *fp_echo, const char *fmt, ... )
{
    va_list v;
    int r;

    va_start( v, fmt );
    vfprintf( fp_echo, fmt, v );
    va_end( v );

    va_start( v, fmt );
    r = vprintf( fmt, v );
    va_end( v );

    return r;
}

There is also a macro named va_arg() that returns successive arguments
of a va_list, given the data type of each argument.  You must determine
what each argument is before calling va_arg().  The following code is
tested and works:

#include <stdio.h>
#include <stdarg.h>

void var_ints( int howmany, ... )
{
    va_list v;
    int i;

    va_start( v, howmany );
    for ( i = 0; i < howmany; i++ )
        printf( "%d ", va_arg( v, int ) );
    va_end( v );
    printf( "\n" );
    return;
}

int main( void )
{
    var_ints( 2, 3, 4 );
    var_ints( 4, 10, 8, 4, 11 );
    var_ints( 0 );
    var_ints( 10, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 );
    return 0;
}

For some reason, the documentation for the va_* macros was omitted from
the libc.inf for DJGPP v2.01.  Hopefully it'll be in the next version.

hth!

-- 
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|      John M. Aldrich       | "A 'critic' is a man who creates     |
|       aka Fighteer I       | nothing and thereby feels qualified  |
|   mailto:fighteer AT cs DOT com   | to judge the work of creative men."  |
| http://www.cs.com/fighteer |               - Lazarus Long         |
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