VARARGS(3)              COMMAND REFERENCE              VARARGS(3)



NAME
     varargs - variable argument list

SYNOPSIS
     #include <varargs.h>

     function( va_alist )
     va_dcl
     va_list pvar ;
     va_start( pvar );
     f = va_arg( pvar , type );
     va_end( pvar );

DESCRIPTION
     This set of macros provides a means of writing portable
     procedures that accept variable argument lists.  Routines
     having variable argument lists (such as printf(3s)) that do
     not use varargs are inherently nonportable, since different
     machines use different argument passing conventions.

     Va_alist  is used in a function header to declare a variable
               argument list.

     Va_dcl    is a declaration for va_alist.  Note that there is
               no semicolon after va_dcl.

     Va_list   is a type which can be used for the variable pvar,
               which is used to traverse the list.  One such
               variable must always be declared.

     Va_start(pvar)
               is called to initialize pvar to the beginning of
               the list.

     Va_arg(pvar, type)
               will return the next argument in the list pointed
               to by pvar.  Type is the type the argument it is
               expected to be.  Different types can be mixed, but
               it is up to the routine to know what type of
               argument is expected, since it cannot be
               determined at run-time.

     Va_end(pvar)
               is used to finish up.

     Multiple traversals, each bracketted by va_start ...
     va_end, are possible.

EXAMPLES
     The following subroutine executes the given filename with
     the given arguments.  The first argument must be a filename,
     and the last argument must be a 0.



Printed 3/13/89                                                 1

VARARGS(3)              COMMAND REFERENCE              VARARGS(3)



          #include <varargs.h>
          execl(va_alist)
          va_dcl
          {
          va_list ap;
          char *filename;
          char *args[100];
          int argno = 0;

          va_start(ap);
          filename = va_arg(ap, char *);
          while (args[argno++] = va_arg(ap, char *))
          ;
          va_end(ap);
          return execv(filename, args);
          }

CAVEATS
     It is up to the calling routine to determine how many
     arguments there are, since it is not possible to determine
     this from the stack frame. For example, execl passes a 0 to
     signal the end of the list.  Printf can tell how many
     arguments are supposed to be there by the format.

SEE ALSO
     nargs(3c).





























Printed 3/13/89                                                 2

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