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 portable functions that accept variable
       argument lists to be written. Functions 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 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  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 corresponding 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 character 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 function.

       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)