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    The following form allows you to view linux man pages.

    Command:

    stdarg

    
    
    

    SYNOPSIS

           #include <stdarg.h>
    
           void va_start(va_list ap, last);
           type va_arg(va_list ap, type);
           void va_end(va_list ap);
           void va_copy(va_list dest, va_list src);
    
    
    

    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().
    
       va_start()
           The  va_start() macro initializes ap for subsequent use by va_arg() and
           va_end(), and must be called first.
    
           The argument last is the name of the last argument before the  variable
           argument list, that is, the last argument of which the calling function
           knows the type.
    
           Because the address of this argument may  be  used  in  the  va_start()
           macro,  it should not be declared as a register variable, or as a func-
           tion or an array type.
    
       va_arg()
           The va_arg() macro expands to an expression that has the type and value
           of  the  next  argument in the call.  The argument 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 argument 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.
    
           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.
    
           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.
    
           If  ap is passed to a function that uses va_arg(ap,type) then the value
           of ap is undefined after the return of that function.
    
       va_end()
           Each invocation of va_start() must be matched by a corresponding  invo-
           cation of va_end() in the same function.  After the call va_end(ap) the
           variable ap is undefined.  Multiple traversals of the list, each brack-
    
           Unfortunately, there are also systems that make it an array of pointers
           (of length 1), and there one needs
    
               va_list aq;
               *aq = *ap;
    
           Finally, on systems where arguments are passed in registers, it may  be
           necessary for va_start() to allocate memory, store the arguments there,
           and also an indication of which argument is next, so that va_arg()  can
           step  through  the  list.   Now  va_end() can free the allocated memory
           again.  To accommodate this situation, C99 adds a macro  va_copy(),  so
           that the above assignment can be replaced by
    
               va_list aq;
               va_copy(aq, ap);
               ...
               va_end(aq);
    
           Each invocation of va_copy() must be matched by a corresponding invoca-
           tion of va_end() in the same function.  Some systems that do not supply
           va_copy()  have  __va_copy instead, since that was the name used in the
           draft proposal.
    
    
    

    ATTRIBUTES

       Multithreading (see pthreads(7))
           The va_start(), va_arg(), va_end(), and va_copy()  macros  are  thread-
           safe.
    
    
    

    CONFORMING TO

           The  va_start(),  va_arg(),  and  va_end()  macros conform to C89.  C99
           defines the va_copy() macro.
    
    
    

    NOTES

           These macros are not compatible with the historic macros they  replace.
           A  backward-compatible  version  can  be  found  in  the  include  file
           <varargs.h>.
    
           The historic setup is:
    
               #include <varargs.h>
    
               void
               foo(va_alist)
                   va_dcl
               {
                   va_list ap;
    
                   va_start(ap);
                   while (...) {
                       ...
                       x = va_arg(ap, type);
    
           their arguments on to a function that takes a va_list argument, such as
           vfprintf(3).
    
    
    

    EXAMPLE

           The function foo takes a string of format characters and prints out the
           argument associated with each format character based on the type.
    
           #include <stdio.h>
           #include <stdarg.h>
    
           void
           foo(char *fmt, ...)
           {
               va_list ap;
               int d;
               char c, *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);
           }
    
                                      2013-12-10                         STDARG(3)
    
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