stdarg(5)                                                         stdarg(5)




 NAME    [Toc]    [Back]
      stdarg.h - macros for handling variable argument lists

 SYNOPSIS    [Toc]    [Back]
      #include <stdarg.h>

      void va_start(va_list pvar, argN);
      type va_arg(va_list pvar, type);
      void va_end(va_list pvar);

 DESCRIPTION    [Toc]    [Back]
      The <stdarg.h> header contains a set of macros that can be used to
      write portable procedures that accept variable argument lists.
      Routines that have variable argument lists (such as printf()) but do
      not use stdarg are inherently nonportable, because different machines
      use different argument-passing conventions.

      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.
      The type of argN should be the same as the argument to the function
      just before the variable portion of the argument list.

      va_arg returns 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, because it cannot be determined at runtime.

      va_end is used to clean up.

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

      NOTE: The <stdarg.h> header file supercedes the <varargs.h> header,
      and contains all of the varargs macros.  <varargs.h> is provided for
      compatibility with pre-ANSI compilers and earlier releases of HP
      C/HP-UX.

 EXAMPLE    [Toc]    [Back]
      This example is a possible implementation of execl (see exec(2)):

           #include <stdarg.h>
           #define MAXARGS 100

           /*  execl is called by
               execl(file, arg1, arg2, ..., (char *)0);
           */
           execl(const char *file, const char *args, ...)
           {
               va_list ap;
               char *array[MAXARGS];



 Hewlett-Packard Company            - 1 -   HP-UX 11i Version 2: August 2003






 stdarg(5)                                                         stdarg(5)




               int argno = 0;

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

 WARNINGS    [Toc]    [Back]
      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, and printf() can tell how many arguments are there by
      the format string.

      Unless ANSI C is used, it is non-portable to specify a second argument
      of char, short, or float to va_arg, because arguments seen by the
      called function are never char, short, or float.

      Pre-ANSI C converts char and short arguments to int and converts float
      arguments to double before passing them to a function.

 SEE ALSO    [Toc]    [Back]
      exec(2), vprintf(3S), varargs(5).

 STANDARDS CONFORMANCE    [Toc]    [Back]
      <stdarg.h>: AES, SVID3, XPG4, FIPS 151-2, POSIX.1, ANSI C

      va_arg: SVID3, XPG4, ANSI C

      va_end: SVID3, XPG4, ANSI C

      va_list: SVID3, XPG4, ANSI C

      va_start: SVID3, XPG4, ANSI C


 Hewlett-Packard Company            - 2 -   HP-UX 11i Version 2: August 2003