There is no such thing as pass by reference in c.  Only pass by
value, even it that value happens to be the address of an object
that the called function is to modify.

In general, if you want a called function to modify an existing
copy of an object, you pass the address of that object to the
function, which of course, must expect to receive a pointer to
the that type of object.

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

#define ASSIGN 0            

char *bar( void)
   {
   static char s[] = "The static string from bar().";
   return s;
   }

void foo(int OP, ...)
   {

   va_list argp; /* points to each unnamed argument in turn*/
   char **ptr;

   va_start(argp, OP);
   ptr = va_arg( argp, char** );
   switch(OP)
      {
      case ASSIGN:
         /* here I want to assign the retrun value of function bar
               to the passed in arg 'str', but I haven't a clue
               how to do it. Is it possible?*/
         *ptr = bar();
         break;

      default:
         *ptr = (char*)NULL;
      }

   va_end(argp);
   return;

   }

int main(void)
   {
   char *str;
   foo(ASSIGN, &str);
   printf("Back from foo, str is: %s\n", str);

   return 0;
   }

--
John R Buchan           -:|:-     Looking for that elusive FAQ?  ftp to: