NAME

       stdarg - variable argument lists

SYNOPSIS

       #include <stdarg.h>

       void va_start( va_list ap, last);
       type va_arg( va_list ap, type);
       void va_end( va_list ap);

DESCRIPTION

       A function may be called with a varying number of arguments of varying types.  The include
       file stdarg.h declares a type va_list and defines three macros for stepping through a list
       of arguments whose number and types are not known to the called function.

       The  called  function  must  declare an object of type va_list which is used by the macros
       va_start, va_arg, and va_end.

       The va_start macro initializes ap for subsequent use by va_arg and  va_end,  and  must  be
       called first.

       The  parameter  last  is the name of the last parameter before the variable argument list,
       i.e., the last parameter of which the calling function knows the type.

       Because the address of this parameter is used in the va_start  macro,  it  should  not  be
       declared as a register variable, or as a function or an array type.

       The va_start macro returns no value.

       The va_arg macro expands to an expression that has the type and value of the next argument
       in the call.  The parameter ap is the va_list ap initialized by va_start.   Each  call  to
       va_arg modifies ap so that the next call returns the next argument.  The parameter type is
       a type name specified so that the type of a pointer to an object that  has  the  specified
       type can be obtained simply by adding a * to type.

       If  there  is  no  next argument, or if type is not compatible with the type of the actual
       next argument (as promoted according to the default argument  promotions),  random  errors
       will occur.

       The  first  use  of the va_arg macro after that of the va_start macro returns the argument
       after last.  Successive invocations return the values of the remaining arguments.

       The va_end macro handles a normal return from the function whose  variable  argument  list
       was initialized by va_start.

       The va_end macro returns no value.

EXAMPLES

       The  function  foo  takes  a  string  of  format  characters  and  prints out the argument
       associated with each format character based on the type.
              void foo(char *fmt, ...)
              {
                   va_list ap;
                   int d;
                   char c, *p, *s;

                   va_start(ap, fmt);
                   while (*fmt)
                        switch(*fmt++) {
                        case 's':           /* string */
                             s = va_arg(ap, char *);
                             printf("string %s\n", s);
                             break;
                        case 'd':           /* int */
                             d = va_arg(ap, int);
                             printf("int %d\n", d);
                             break;
                        case 'c':           /* char */
                             /* need a cast here since va_arg only
                                takes fully promoted types */
                             c = (char) va_arg(ap, int);
                             printf("char %c\n", c);
                             break;
                        }
                   va_end(ap);
              }

CONFORMING TO

       The va_start, va_arg, and va_end macros conform to ANSI X3.159-1989 (``ANSI C'').

COMPATIBILITY

       These macros are not compatible  with  the  historic  macros  they  replace.   A  backward
       compatible version can be found in the include file varargs.h.

BUGS

       Unlike  the varargs macros, the stdarg macros do not permit programmers to code a function
       with no fixed arguments.  This problem generates work mainly when converting varargs  code
       to  stdarg code, but it also creates difficulties for variadic functions that wish to pass
       all of their  arguments  on  to  a  function  that  takes  a  va_list  argument,  such  as
       vfprintf(3).