J3/14-135r3
To: J3
Subject: Poor exposition for OPEN statement modifying current connection
From: Van Snyder
Date: 2014 June 25
Reference: 14-123r2

1. Introduction
===============

Subclause 9.5.6.1p6 says

  "If the file to be connected to the unit is the same as the file to
  which the file is connected, only the changeable modes (9.5.2) may
  have values different from those of the existing connection."

It's not clear what a "value of the existing connection" is.  That
paragraph continues to give explicit specification for the POSITION= and
STATUS= specifiers, so either they don't specify "values for the
connection" or there's a contradiction.

At the end, it says

  "The ERR=, IOSTAT=, and IOMSG= specifiers from an OPEN statement have
  no effect on any subsequent OPEN statement."

This appears nowhere else.  One might interpret it as yet another
exception to the first sentence, or to mean that if these specifiers do
not appear the ones from the OPEN statement that established the
connection, or from an earlier OPEN statement that modified the
connection, are not used.  If the latter, in light of the words "during
execution of an input/output statement that contains neither the ERR=
nor IOSTAT= specifiers" in 9.11.2p2, it does not appear to be necessary.
The exposition in 9.11.6 could be improved to make this clear in the
IOMSG= case.

It would be better simply to list the specifiers that are not allowed to
specify different values from the ones specified when the current
connection was initially established.

Paper 14-123r2 urged the editor to insert a UTI, but the editor does not
agree that it is a technical issue.

Specification:

Clarify the explanation for OPEN on a connected unit

Syntax:

None.

Edits to 14-007r1


[206:27-35 9.5.6.1p6]  Replace the paragraph:

"If the file to be connected to the unit is the same as the file to which
the unit is currently connected, a new connection is not established and
values for any changeable modes (9.5.2) specified come into effect for
the current connection; the current file position is unaffected.
Before any effect on changeable modes, a wait operation is performed for
any pending asynchronous data transfer operations for the specified unit.
If the POSITION= specifier appears in such an OPEN statement, the value
specified shall not disagree with the current position of the file. If
the STATUS= specifier is included in such an OPEN statement, it shall
be specified with the value OLD. Other than ERR=, IOSTAT= and IOMSG=,
all other specifiers in such an OPEN statement shall not differ from
those in effect for the current connection."