Designates a variable to store a value indicating the status of a
  data transfer operation.  It takes the following form:

  IOSTAT = ios

  ios   Is a scalar default integer variable.

  If no error exists, "ios" is defined as zero.  If an error exists,
  "ios" is defined as a positive integer.

  IOSTAT applies only to the OPEN statement in which it appears and
  not to subsequent I/O operations on the logical unit that is
  opened.  However, you can use the IOSTAT parameter in subsequent
  I/O statements to perform a similar function.

  Secondary operating system messages do not display when IOSTAT is
  specified.  To display these messages, remove IOSTAT or use a
  platform-specific method such as a VMS condition handler.  (For
  more information, see the HP Fortran for OpenVMS User Manual.)