I have a stupid question: how does D handle variable length argument lists? I've been over the D document and didn't see anything on it unless I missed something.

Thanks,
Ted

"Ted Williams" <ted.wil.no.spam@verizon.net> wrote in message news:c8m1t8$1gan$1@digitaldaemon.com...
> I have a stupid question: how does D handle variable length argument
lists?
> I've been over the D document and didn't see anything on it unless I
missed
> something.

It handles them exactly as you'd handle them in C. You can also use std.c.stdarg.

I have tried to use the templates in the std.c.stdarg package.  I cant get
the code to compile.
The following snippet illustrates the problem:

import std.c.stdarg;

void TestArgs( char[] format, ... )
{
    va_list args;

    alias va_start!( char[] ) s;
    alias va_arg!(Object) a;

    s.va_start( args, format );
    Object o = a.va_arg( args );
}

When compiled I get the following errors:

args.d(11): function va_start (va_list ap,char[]parmn) does not match
argument types ()
args.d(11): Error: expected 2 arguments, not 0
args.d(11): no property 'va_start' for type 'void'

What am I doing wrong?

Thanks,
Ted

Ted Williams wrote:

>I have tried to use the templates in the std.c.stdarg package.  I cant get
>the code to compile.
>The following snippet illustrates the problem:
>
>import std.c.stdarg;
>
>void TestArgs( char[] format, ... )
>{
>    va_list args;
>
>    alias va_start!( char[] ) s;
>    alias va_arg!(Object) a;
>
>    s.va_start( args, format );
>    Object o = a.va_arg( args );
>}
>
>When compiled I get the following errors:
>
>args.d(11): function va_start (va_list ap,char[]parmn) does not match
>argument types ()
>args.d(11): Error: expected 2 arguments, not 0
>args.d(11): no property 'va_start' for type 'void'
>
>What am I doing wrong?
>
>Thanks,
>Ted
>
>
>  
>
void TestArgs( char[] format, ... )
{
  va_list args;

  alias va_start!( char[] ) s;
  alias va_arg!(Object) a;

  s( args, format );
  Object o = a( args );
}

-- 
-Anderson: http://badmama.com.au/~anderson/

Ted Williams wrote:
> I have tried to use the templates in the std.c.stdarg package.  I cant get
> the code to compile.
> The following snippet illustrates the problem:
> 
> import std.c.stdarg;
> 
> void TestArgs( char[] format, ... )
> {
>     va_list args;
> 
>     alias va_start!( char[] ) s;
>     alias va_arg!(Object) a;
> 
>     s.va_start( args, format );
>     Object o = a.va_arg( args );
> }

Try this instead:
    s( args, format );
    Object o = a( args );

> When compiled I get the following errors:
> 
> args.d(11): function va_start (va_list ap,char[]parmn) does not match
> argument types ()
> args.d(11): Error: expected 2 arguments, not 0
> args.d(11): no property 'va_start' for type 'void'
> 
> What am I doing wrong?
> 
> Thanks,
> Ted
> 
> 

Ted Williams wrote:
> I have tried to use the templates in the std.c.stdarg package.  I cant get
> the code to compile.
> The following snippet illustrates the problem:
> 
> import std.c.stdarg;
> 
> void TestArgs( char[] format, ... )
> {
>     va_list args;
> 
>     alias va_start!( char[] ) s;
>     alias va_arg!(Object) a;
> 
>     s.va_start( args, format );
>     Object o = a.va_arg( args );
> }
> 
> When compiled I get the following errors:
> 
> args.d(11): function va_start (va_list ap,char[]parmn) does not match
> argument types ()
> args.d(11): Error: expected 2 arguments, not 0
> args.d(11): no property 'va_start' for type 'void'
> 
> What am I doing wrong?
> 
> Thanks,
> Ted

I don't know why your code doesn't compile. But here's an example that Walter posted earlier that does seem to work:

import std.c.stdarg;

int foo(char *x, ...)
{
    va_list ap;

    va_start!(typeof(x))(ap, x);
    printf("&x = %p, ap = %p\n", &x, ap);

    int i;
    i = va_arg!(typeof(i))(ap);
    printf("i = %d\n", i);

    long l;
    l = va_arg!(typeof(l))(ap);
    printf("l = %lld\n", l);

    uint k;
    k = va_arg!(typeof(k))(ap);
    printf("k = %u\n", k);

    va_end(ap);

    return i + l + k;
}

void main()
{
    int j;

    j = foo("hello", 3, 23L, 4);
    printf("j = %d\n", j);
    assert(j == 30);
}

/*
adapted from http://www.digitalmars.com/drn-bin/wwwnews?digitalmars.D/273
*/

-- 
Justin (a/k/a jcc7)
http://jcc_7.tripod.com/d/

Ted Williams wrote:
> I have tried to use the templates in the std.c.stdarg package.  I cant get
> the code to compile.
> The following snippet illustrates the problem:
> 
> import std.c.stdarg;
> 
> void TestArgs( char[] format, ... )
> {
>     va_list args;
> 
>     alias va_start!( char[] ) s;
>     alias va_arg!(Object) a;
> 
>     s.va_start( args, format );
>     Object o = a.va_arg( args );
> }

You do realize that you don't HAVE to use aliases, don't you? D's templates have been upgraded a while back to allow convenient use without the need for those aliases.

I'm just asking because lately I've seen aliases used a lot where they don't seem necessary.

The following would work:

void TestArgs( char[] format, ... )
{
    va_list args;

    va_start!(char[])(args, format );
    Object o = va_arg!(Object)( args );
}


Hauke

Ted Williams wrote:

> I have tried to use the templates in the std.c.stdarg package.  I cant get
> the code to compile.
<snip>
> What am I doing wrong?

IMHO, trying to do D stuff with a syntax feature that was presumably only put in for interfacing to C.  (My guess is that the templates were put in there for the sake of completeness rather than anything else.)

Mabye there are better solutions, or maybe it's better to wait for D to have its own, built-in support for VALs....

Stewart.

-- 
My e-mail is valid but not my primary mailbox, aside from its being the unfortunate victim of intensive mail-bombing at the moment.  Please keep replies on the 'group where everyone may benefit.