From: see@... (Douglas Wells)
Date: 2007-03-19T09:15:04+09:00
Subject: Re: Problem trying to use varargs in private function within C extension

In article <1174230439.978761.157660@b75g2000hsg.googlegroups.com>,
"Daniel Berger" <djberg96@gmail.com> writes:
> Hi all,
> 
> Ruby 1.8.6
> Windows XP
> VC++ 8
> 
> This simple C extension complains of "too few arguments for call" when
> I try to build it. Yet, within a standalone C program it works fine.
> Am I forced to use varargs.h instead of stdarg.h? If so, how do I make
> this work? The varargs.h docs confuse me.

Let me add a few comments in addition to Patrick Hurley's correction (in
<554ac39c0703180901u6db598dch277233129e509b79@mail.gmail.com>):

First, varargs.h will not help.  In fact, you don't even need
stdarg.h until you actually start to reference the arguments using
the appropriate macros.

Second, turn on the compiler diagnostics.  *Both* of your programs
below are not legal C and any reasonable compiler should diagnose
the problem(s).  In particular, your declarations and definitions
of "test" differ.  Your declaration declares the procedure to have
one mandatory argument; your definition requires that there are
two mandatory arguments.  These are inconsistent (and thus illegal).

Third, relevant to Patrick's correction, note that your "stand-alone"
test case is not at all the same as the in-context code (the number
of arguments supplied is different).

> #include <ruby.h>
> #include <stdarg.h>
> 
> int test(const char*, ...);

> /* String mandatory, encoding optional */
> int test(const char* str, int encoding, ...){
>    int total = 0;
>    total = encoding;
> 
>    printf("X: %s\n", str);
>    printf("Encoding: %i\n", encoding);
> 
>    return total;
> }

Running with spirit of this comment:

/* String mandatory, encoding optional */
int test(const char* x, ...){
   va_list ap;
   int total = 0;
   int encoding;

   va_start (ap, x);
   encoding = va_arg(ap, int);
   va_end(ap);

   total = encoding;

   printf("Encoding: %i\n", encoding);

   return total;
}

> static VALUE foo_test(VALUE self){
>    int total = 0;
> 
>    total = test("hello"); /* Failure! */
>    printf("TOTAL: %i\n");
>    return self;
> }
> 
> void Init_foo(){
>    VALUE cFoo = rb_define_class("Foo", rb_cObject);
>    rb_define_method(cFoo, "test", foo_test, 0);
> }
> 
> And here's the standalone C code that builds and runs fine:

Just because it builds and runs fine doesn't mean that it isn't
wrong. That mind set just leads to future problems.

> #include <windows.h>
> #include <stdio.h>
> #include <stdarg.h>
> 
> int test(const char*, ...);
> 
> int main(){
>    int val = 0;
> 
>    val = test("hello", 3);
>    printf("VAL: %i\n", val);
> 
>    return 0;
> }
> 
> int test(const char* x, int encoding, ...){
>    int total = 0;
>    total = encoding;
> 
>    printf("Encoding: %i\n", encoding);
> 
>    return total;
> }
> 
> Dan

 - dmw


-- 
.   Douglas Wells             .  Connection Technologies      .
.   Internet:  -sp9804- -at - contek.com-                     .