J3/04-306r1

Date:  6-May-2004
To:    J3
From:  JOR/interp/Stan Whitlock
Subj:  F95 interpretation #000068


NUMBER: 000068
TITLE: Asterisks as I/O units
KEYWORDS: Asterisk, I/O, unit
DEFECT TYPE: Erratum
STATUS: J3 consideration in progress

Question:

1.   Does the Fortran 95 standard require the external unit
     corresponding to the I/O unit identified by an asterisk for
     input or output to be the same as the external unit identified
     by some fixed nonnegative integer value?

2.   Can the I/O unit identified by an asterisk for input or output
     correspond to more than one external unit?

3.   If the external unit identified by an integer value that
     corresponds to the I/O unit identified by an asterisk for input
     or output is closed, does that cause the I/O unit identified by
     an asterisk to become disconnected?

ANSWER:

     1.   No.

     2.   No.

     3.   Not addressed by Fortran 95.

DISCUSSION:

The submitter states:  At least one Fortran 95 implementation uses -1
as the value of the I/O unit identified by an asterisk.  A carefully
constructed INQUIRE statement can expose this value to the user.  Many
users expect I/O to the units identified by asterisks to continue to
work even after the corresponding units identified by integer values
have been closed.

     1.   There is no requirement in the standard that the asterisk
correspond to an external-file-unit; it is, however, permissible.

     2.   For the units identified by the asterisk, the text of
section 9.3.2 does not allow two or more units to be connected
simultaneously to the same file [139:8-9].

     3.   Fortran 95 does not specify the behavior in this instance.

REFERENCES:  ISO/IEC 1539-1:1997(E), Sections 9.3 and 9.4.4.2

EDITS:  None

SUBMITTED BY: Robert Corbett

HISTORY:  99-192    m150  Submitted
          99-215r1  m150  approved uc
          00-208    m153  passed by J3 letter ballot
          00-268    m154  Failed WG5 letter ballot (N1395 & N1403)
          WG5/N1452       Suggested revision (expanded discussion)
          01-296r1  m158  Passed by J3 meeting
          01-380    m159  Failed J3 letter ballot
          04-306r1  m168  Submitted for J3 meeting vote