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<stdarg.h>(P)		   POSIX Programmer's Manual		 <stdarg.h>(P)

PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the	 corresponding
       Linux  manual page for details of Linux behavior), or the interface may
       not be implemented on Linux.

NAME
       stdarg.h - handle variable argument list

SYNOPSIS
       #include <stdarg.h>

       void va_start(va_list ap, argN);
       void va_copy(va_list dest, va_list src);
       type va_arg(va_list ap, type);
       void va_end(va_list ap);

DESCRIPTION
       The <stdarg.h> header shall contain a set of macros which allows porta‐
       ble  functions that accept variable argument lists to be written. Func‐
       tions that have variable argument lists (such as printf()) but  do  not
       use  these macros are inherently non-portable, as different systems use
       different argument-passing conventions.

       The type va_list shall be defined for variables used  to	 traverse  the
       list.

       The  va_start()	macro  is invoked to initialize ap to the beginning of
       the list before any calls to va_arg().

       The va_copy() macro initializes dest as	a  copy	 of  src,  as  if  the
       va_start() macro had been applied to dest followed by the same sequence
       of uses of the va_arg() macro as had previously been used to reach  the
       present	state of src. Neither the va_copy() nor va_start() macro shall
       be invoked to reinitialize dest without an  intervening	invocation  of
       the va_end() macro for the same dest.

       The object ap may be passed as an argument to another function; if that
       function invokes the va_arg() macro with parameter ap, the value of  ap
       in  the	calling	 function  is  unspecified  and shall be passed to the
       va_end() macro prior to any further reference to ap. The parameter argN
       is  the identifier of the rightmost parameter in the variable parameter
       list in the function definition (the one just before the ...).  If  the
       parameter  argN	is  declared  with  the register storage class, with a
       function type or array type, or with a type that is not compatible with
       the  type that results after application of the default argument promo‐
       tions, the behavior is undefined.

       The va_arg() macro shall return the next argument in the	 list  pointed
       to by ap. Each invocation of va_arg() modifies ap so that the values of
       successive arguments are returned in turn. The type parameter shall  be
       a type name specified such that the type of a pointer to an object that
       has the specified type can be obtained simply by postfixing  a  '*'  to
       type. If there is no actual next argument, or if type is not compatible
       with the type of the actual next argument (as promoted according to the
       default argument promotions), the behavior is undefined, except for the
       following cases:

	* One type is a signed integer type, the other type is the correspond‐
	  ing  unsigned	 integer  type, and the value is representable in both
	  types.

	* One type is a pointer to void and the other is a pointer to a	 char‐
	  acter type.

	* Both types are pointers.

       Different  types can be mixed, but it is up to the routine to know what
       type of argument is expected.

       The va_end() macro is used to clean  up;	 it  invalidates  ap  for  use
       (unless va_start() or va_copy() is invoked again).

       Each invocation of the va_start() and va_copy() macros shall be matched
       by a corresponding invocation of the va_end() macro in the  same	 func‐
       tion.

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

EXAMPLES
       This example is a possible implementation of execl():

	      #include <stdarg.h>

	      #define  MAXARGS	   31

	      /*
	       * execl is called by
	       * execl(file, arg1, arg2, ..., (char *)(0));
	       */
	      int execl(const char *file, const char *args, ...)
	      {
		  va_list ap;
		  char *array[MAXARGS +1];
		  int argno = 0;

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

       The following sections are informative.

APPLICATION USAGE
       It is up to the calling routine to communicate to  the  called  routine
       how  many  arguments there are, since it is not always possible for the
       called routine to determine  this  in  any  other  way.	 For  example,
       execl()	is  passed  a  null pointer to signal the end of the list. The
       printf() function can tell how many arguments are there by  the	format
       argument.

RATIONALE
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       The System Interfaces volume of IEEE Std 1003.1-2001, exec, printf()

COPYRIGHT
       Portions	 of  this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
       --  Portable  Operating	System	Interface (POSIX), The Open Group Base
       Specifications Issue 6, Copyright (C) 2001-2003	by  the	 Institute  of
       Electrical  and	Electronics  Engineers, Inc and The Open Group. In the
       event of any discrepancy between this version and the original IEEE and
       The  Open Group Standard, the original IEEE and The Open Group Standard
       is the referee document. The original Standard can be  obtained	online
       at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group		     2003			 <stdarg.h>(P)
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