VARARGS(5)                           SysV                           VARARGS(5)



NAME
     varargs - handle variable argument list

SYNOPSIS
     #include <varargs.h>

     va_alist

     va_dcl

     void va_start(pvar)
     va_list pvar;

     type va_arg(pvar, type)
     va_list pvar;

     void va_end(pvar)
     va_list pvar;

DESCRIPTION
     These macros are obsolete.  <stdarg.h> defines their standard C
     compatible namesakes.  See stdarg(3C).

     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.

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

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

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

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

     va_arg 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.

     va_end 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>
     #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), stdarg(3C).

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.