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stdarg.h(0P)		   POSIX Programmer's Manual		  stdarg.h(0P)

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 functionality described on this reference page is aligned with  the
       ISO C  standard.	 Any  conflict between the requirements described here
       and the ISO C standard is unintentional. This  volume  of  POSIX.1‐2008
       defers to the ISO C standard.

       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  <stdarg.h> header shall define the va_list type 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 promotions, 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 compat‐
       ible  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 corre‐
	   sponding 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.

       The following sections are informative.

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);
	   }

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 POSIX.1‐2008, exec, fprintf()

COPYRIGHT
       Portions	 of  this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
       --  Portable  Operating	System	Interface (POSIX), The Open Group Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
       cal  and	 Electronics  Engineers,  Inc  and  The	 Open Group.  (This is
       POSIX.1-2008 with the 2013 Technical Corrigendum	 1  applied.)  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.unix.org/online.html .

       Any typographical or formatting errors that appear  in  this  page  are
       most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors,	 see  https://www.ker‐
       nel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group		     2013			  stdarg.h(0P)
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