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    STDARG(3)           Linux Programmer's Manual           STDARG(3)

    NAME
           stdarg - variable argument lists

    SYNOPSIS
           #include <stdarg.h>

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

    DESCRIPTION
           A  function  may  be called with a varying number of argu-
           ments  of  varying  types.   The  include  file   stdarg.h
           declares a type va_list and defines three macros for step-
           ping 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 parame-
           ter 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.  Succes-
           sive invocations return the values of the remaining  argu-
           ments.

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

    BSD MANPAGE              29 November 1993                       1

    STDARG(3)           Linux Programmer's Manual           STDARG(3)

           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  char-
           acter 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 */
                                 c = va_arg(ap, char);
                                 printf("char %c\n", c);
                                 break;
                            }
                       va_end(ap);
                  }

    STANDARDS
           The  va_start,  va_arg,  and va_end macros conform to ANSI
           C3.159-1989 (``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  argu-
           ments on to a function that takes a va_list argument, such
           as vfprintf(3).

    BSD MANPAGE              29 November 1993                       2

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