varargs(5)                 DG/UX 4.30                  varargs(5)



     NAME
          varargs - handle variable argument list

     SYNOPSIS
          #include <varargs.h>

          vaalist

          vadcl

          void vastart(pvar)
          valist pvar;

          type vaarg(pvar, type)
          valist pvar;

          void vaend(pvar)
          valist pvar;

     DESCRIPTION
          This set of macros allows portable procedures that accept
          variable argument lists to be written.  Routines that have
          variable argument lists [such as printf(3S)] but do not use
          varargs are inherently nonportable, as different machines
          use different argument-passing conventions.

          vaalist is used as the parameter list in a function header.

          vadcl is a declaration for va_alist.  No semicolon should
          follow va_dcl.

          valist is a type defined for the variable used to traverse
          the list.

          vastart is called to initialize pvar to the beginning of
          the list.

          vaarg will return the next argument in the list pointed to
          by pvar.  Type is the type the argument is expected to be.
          Different types can be mixed, but it is up to the routine to
          know what type of argument is expected, as it cannot be
          determined at runtime.

          vaend is used to clean up.

          Multiple traversals, each bracketed by va_start ...  va_end,
          are possible.

     EXAMPLE
          This example is a possible implementation of execl(2).

               #include <varargs.h>



     Licensed material--property of copyright holder(s)         Page 1

     varargs(5)                 DG/UX 4.30                  varargs(5)



               #define MAXARGS     100

               /*   execl is called by
                         execl(file, arg1, arg2, ..., (char *)0);
               */
               execl(va_alist)
               va_dcl
               {
                    va_list ap;
                    char *file;
                    char *args[MAXARGS];
                    int argno = 0;

                    va_start(ap);
                    file = va_arg(ap, char *);
                    while ((args[argno++] = va_arg(ap, char *)) != (char *)0)
                         ;
                    va_end(ap);
                    return execv(file, args);
               }

     SEE ALSO
          exec(2), printf(3S), vprintf(3S).

     NOTES
          It is up to the calling routine to specify how many
          arguments there are, since it is not always possible to
          determine this from the stack frame.  For example, execl is
          passed a zero pointer to signal the end of the list.  Printf
          can tell how many arguments are there by the format.
          It is non-portable to specify a second argument of char,
          short, or float to va_arg, since arguments seen by the
          called function are not char, short, or float.  C converts
          char and short arguments to int and converts float arguments
          to double before passing them to a function.




















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