VMS Help CC, Run-time functions, fcntl  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  Performs controlling operations on an open file specified by the
  file_desc parameter.  The values for the request parameter are
  defined in the <fcntl.h> header file.

  Syntax:

       #include <sys/types.h>
       #include <unistd.h>
       #include <fcntl.h>

       int fcntl(int file_desc, int request [, int file_desc2]);