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From: "David H. Haley" <dhaley@onlink.net>
Subject: Help With Ada_Io and Exceptions
Date: 1997/05/29
Message-ID: <338E3601.3E7E@onlink.net>#1/1
X-Deja-AN: 244859078
References: <338CEEA4.93867B6D@iinet.net.au>
Organization: Ontario Northland--ONLink
Reply-To: dhaley@onlink.net
Newsgroups: comp.lang.ada
Date: 1997-05-29T00:00:00+00:00
List-Id: <comp.lang.ada>


-- I'm having a bit of a problem with Ada_Io.get after a Data_Error is
raised,
-- and am wondering if anyone can shed some light on this.

-- Many thanks in advance...... 

WITH Ada_Io; USE Ada_Io; 
WITH Text_Io; USE Text_Io; 
--
-- adapted from ADA as a second language
-- by Norman H. Cohen Page 485
--
-- The purpose of this procedure is to check to see whether or not
-- the user has input valid data - i.e. an integer is expected; however,
-- if the user enters a character string e.g. "t" or "test" in lieu of
-- the expected integer, then the procedure should inform the user
-- of his/her error and prompt for correct data input
--
PROCEDURE T IS 
   My_Number          : Integer;
   Well_Formed_Number : Boolean; 
BEGIN
   Ada_Io.Put("Please enter a number between 1 and 10  "); 
   LOOP
      BEGIN
	 Ada_Io.Put("=> ");
	 Ada_Io.Get(My_Number); 
	 --
	 --              ***** Problem Area ****
	 --
	 -- if a keyboard character(s) is entered, i.e. "t" or "test"
	 -- the Exception Handler catches the Data_Error, then
	 -- the program will loop back up to the above two statements;
	 -- however, while the Put statement is correctly executed
	 -- the Get statment does not permitted any data entry and
	 -- the program endlessly loops. (An examination of the
	 -- assembly listing shows that the .asm file produced loops
	 -- back to the correct position; however, I have not
	 -- used an assembler to see if the expected action
	 -- actually occurs).
	 --
	 -- Thus, what is displayed after a character i.e. "t" is
	 -- entered is:
	 --             An error occurred
	 --             That is not a number
	 --             Please re-enter => An error occurred
	 --             That is not a number
	 --             Please re-enter => An error occurred
	 --             That is not a number
	 --             ...
	 --
	 -- the same situation occurs with Ada_Io and the Meridian
	 -- pre-defined library package Iio which consists of an
	 -- instantiation of Text_Io.Integer_Io for the standard
	 -- type integer
	 --
	 -- On page 635 of Cohen's book he states "As soon as
	 -- an unexpected character or terminator is encountered,
	 -- Get raises Data_Error, and no further characters are
	 -- read. The offending character or terminator remains
	 -- unread and can be processed by a subsequent input
	 -- operation if Data_Error is handled
	 --
	 -- Note that if you enter a number such as "888888888"
	 -- then the program loops as expected (in that it allows
	 -- a further entry of data in the Get statement)
	 -- after outputting the following error messages:
	 --
	 --            An error occurred
	 --            That is not a number
	 --
	 Well_Formed_Number := True; 
      EXCEPTION
	 WHEN Data_Error => 
	    Well_Formed_Number := False; 
	    Ada_Io.Put_Line("An error occurred"); 
	 WHEN OTHERS => 
	    Ada_Io.Put_Line("Program Abnormally Terminated"); 
      END; 
      EXIT WHEN Well_Formed_Number AND THEN My_Number IN 1 .. 10; 
      IF Well_Formed_Number THEN 
	 Ada_Io.Put_Line("That is not between 1 and 10."); 
      ELSE 
	 Ada_Io.Put_Line("That is not a number."); 
      END IF; 
      Ada_Io.Put("Please re-enter"); 
      DELAY (1.0);  -- for illustration purposes only
   END LOOP; 
END T;