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From: ram@zedat.fu-berlin.de (Stefan Ram)
Newsgroups: comp.lang.c
Subject: Re: is it possible to have functions with 0, 1, or 2 args?
Date: 5 Aug 2024 09:06:42 GMT
Organization: Stefan Ram
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Expires: 1 Jul 2025 11:59:58 GMT
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Mark Summerfield <mark@qtrac.eu> wrote or quoted:
>The rational is that I'd like to create a function `new_thing()` which
>takes an optional size, e.g.,

  I'm hella stoked on writing code that's chill in C. So,
  in a sitch like this, I might roll with a function that's
  /always/ down to take an argument and just hit it with a
  "-1" if I'm not trying to lock down a size.

  The "va_list" jazz in C, courtesy of the <stdarg.h> header, lets
  functions roll with a flexible number of args. It's like a buffet
  line for arguments, where you can scoop them up one by one using
  those gnarly macros "va_start", "va_arg", and "va_end". 

  But here's the rub - the function's not psychic, so it can't just
  divine how many args are coming down the pike. You got to clue it in
  somehow, like passing a head count or dropping a hint about where to
  pump the brakes. The coder doesn't have to play bean counter though;
  he could just slap a "Dead End" sign at the tail of the arg parade!

  main.c

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

int f( int const n, ... ) 
{ va_list args; /* to hold the variable arguments */
  va_start( args, n ); /* Initialize the "va_list" variable with the */
  int result;          /* variable arguments, starting after n       */
  switch( n )
  { case 0: result = f( 2, 3, 11 ); break;
    /* va_arg(args, int) retrieves the next argument from the "va_list"
       of type "int" */
    case 1: result = f( 2, 3, va_arg( args, int )); break; 
    case 2: 
    result = va_arg( args, int )+ va_arg( args, int ); break; }
  va_end( args ); /* Clean up the "va_list" */
  return result; }

int main( void )
{ printf
  ( "%d\n", 14 == f( 0 )&& 8 == f( 1, 5 )&& 11 == f( 2, 2, 9 )); }

  transcript

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