va_arg() -- Variable Arguments

Return pointer to next argument in argument list
#include <stdarg.h>
typename *va_arg(listptr, typename)
va_list listptr, typename;

#include <varargs.h>
typename *va_arg(listptr, typename)
va_list listptr, typename;

va_arg() returns  a pointer to the  next argument in an  argument list.  It
can be used  with functions that take a variable  number of arguments, such
as  printf() or  scanf(), to  help  write such  functions portably.   It is
always used  with va_end()  and va_start() within  a function that  takes a
variable number of arguments.

listptr   is  of   type   va_list,  which   is  defined   in  the   headers
<stdarg.h>   and  <varargs.h>.  This   object  must   first  be
initialized by the macro va_start().

typename is the name of the type for which va_arg() is to return a pointer.
For  example, if  you wish  va_arg()  to return  a pointer  to an  integer,
typename should be of type int.

va_arg() can  only handle ``standard''  data types, i.e.,  those data types
that can be transformed to pointers by appending an asterisk `*'.

Example

For an example of this macro, see the entry for stdarg.h.

See Also

stdarg.h,
varargs.h
ANSI Standard, §7.8.1.2

Notes

There are  two different versions  of va_arg(): the ANSI  version, which is
defined  in <stdarg.h>;  and the  UNIX version,  which is  defined in
<varargs.h>. For  a discussion  of how these  implementations differ,
see the entry for stdarg.h.

If there  is no  next argument  for va_arg() to  handle, or if  typename is
incorrect, then the behavior of va_arg() is undefined.

The ANSI Standard demands that va_arg() be implemented only as a macro.  If
its  macro  definition is  suppressed  within a  program,  its behavior  is
undefined.

© 2012 by Stephen A. Ness