J3/99-261

Date:		30 Nov 1999
From:		Dick Hendrickson
Subject:	Simpler Example of Volatile
References:	99-252, issue 34 [438], issue 83 [7]


Replace section C.2.3 with a simpler example of use of the VOLATILE attribute.  This will eliminate the need for Copyright notices and be easier to follow.  Also add a reference to the C standard in chapter one.

Edites:

Replace page 438, lines 21-53 and page 439 lines 1-49 with:

The following example shows the use of a variable with the VOLATILE attribute to communicate with an asynchronous process, in this case the operating system.  The program detects a user keystroke on the terminal and reacts at a convenient point in its processing.

The VOLATILE attribute is necessary to prevent an optimizing compiler from storing the communication variable in a register or from doing flow analysis and deciding that the EXIT statement can never be executed.

Subroutine Terminate_Iterations

  Logical, VOLATILE  ::   user_hit_any_key
     ...
!  have the OS start to look for a user keystroke and set the variable "user_hit_any_key"
!      to TRUE when it detects a keystroke

    Call operating_system("BEGIN DETECT USER KEYSTROKE", user_hit_any_key)

    user_hit_any_key = .false.           !this will ignore any recent keystrokes
    print *, "hit any key to terminate iterations!"

      Do I = 1,100
        .....   !  compute a value for R
        print *, I, R
        if (user_hit_any_key)  EXIT
      Enddo

!Have the OS stop looking for user keystrokes
  Call operating_system("STOP DETECT USER KEYSTROKE")

End Subroutine Terminate_Iterations

Page 7, line 6, Add
ISO/IEC 9899-1990 Information Technology - Programming Languages - C

We refer to this standard as the C standard.

Page 7, lines 7-11, change the text of note 83 to
When the forthcoming standard revision  of the C standard has been published,
the reference to ISO/IEC 9899-1990 should be updated.