Re: Is this doable in MS C?

From:
"Igor Tandetnik" <itandetnik@mvps.org>
Newsgroups:
microsoft.public.vc.language
Date:
Wed, 10 Dec 2008 20:46:36 -0500
Message-ID:
<ODI3oLzWJHA.5764@TK2MSFTNGP04.phx.gbl>
Tommy <bad@reallybad.com> wrote:

Igor Tandetnik wrote:

Tommy <bad@reallybad.com> wrote:

But the only true variadic method is to go direct with va_list
traversal using a count or terminator method.

For example:

 MY_MACRO(
          count1, fmt1, ...,
          count2, fmt2, ...,
          count3, fmt3, ...,
          .
          .
          countN, fmtN, ...,
          NULL);


Could you show how you would actually implement such a macro? So
that, for example,

MY_MACRO(
    2, "%d %f\n", 1, 2.0,
    2, "%s %s\n", "hello", "world",
    NULL);

prints

1 2.0
hello world


I can't with the macro because as I noted in my initial post:

    I remember once coming across a similar need. If I recall,
    the "design issues" was two folds:

    - Not knowing exactly the true count of the arguments and types,
    - Requiring a count as a previous or a terminator of some sort.

But if you go direct, you can solve it very easily:

void foo(int argc, ...)
{
    va_list argptr;
    va_start(argptr, argc);
    const char *p = NULL;
    while (argc && (p = va_arg(argptr,const char *))) {
       vprintf_s( p, argptr );
       while (argc--) va_arg(argptr, void *); // SEE NOTE1
       argc = va_arg(argptr, int);
    }
    va_end(argptr);
}

#define MY_MACRO foo

 MY_MACRO(
     2, "%d %f\n", 1, 2.0,
     2, "%s %s\n", "hello", "world",
     NULL);


Have you actually tested this code? Does it work for you? It crashes for
me after printing the first line.
--
With best wishes,
    Igor Tandetnik

With sufficient thrust, pigs fly just fine. However, this is not
necessarily a good idea. It is hard to be sure where they are going to
land, and it could be dangerous sitting under them as they fly
overhead. -- RFC 1925

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