Path: utzoo!attcan!uunet!ora!ccavax!merriman
From: merriman@ccavax.camb.com
Newsgroups: comp.lang.pascal
Subject: Re: I/O with VAX Pascal
Message-ID: <25603.266a9279@ccavax.camb.com>
Date: 4 Jun 90 20:55:20 GMT
References: <38995.26678cba@eco.economics.adelaide.edu.au> <1069@umriscc.isc.umr.edu>
Organization: Cambridge Computer Associates, Inc.
Lines: 85

In article <1069@umriscc.isc.umr.edu>, ronp@usenet.umr.edu (Ron Pacheco) writes:
> In article <38995.26678cba@eco.economics.adelaide.edu.au> djung@eco.economics.adelaide.edu.au writes:
>>Question:
>>
>>  Does anyone know the best way (I don't know any way) to do character by
>>character I/O using VAX Pascal?
>>  I wish to write some interactive code - reading arrow keys etc -
>>but VMS buffers I/O, so I don't get any input until the user hits return.
>>
>>Any help or pointers would be appreciated.
>>
>>			Thanks,
>>				-David Jung.
>>
>>   djung@eco.ua.oz.au         (Eco is internet 129.127.4.9)
>>or csdljung@medusa.ua.oz.au   (Medusa is internet 129.127.104.1)
> 
> I have posted an example of reading a single from the terminal in VAX Pascal.
> As previosly mentioned, this cannot be done directly via VAX Pascal statements
> as all I/O (well, most I/O most of the time) is buffered.
> 
> This message contains two source files: READKEY.PAS is a MODULE which contains
> the routines to read keystrokes, DOREADKEY.PAS is a PROGRAM which demonstrates
> the use of the module.
> 
[ stuff deleted]

> 
> [GLOBAL] FUNCTION ReadKey(VAR Key: Integer): Unsigned;
> 
> { This function reads a single keystroke from the keyboard and returns the
>   ASCII code of the key which was pressed. }
> 
> VAR   Ch:   Char;
>       Stat: Unsigned;
> 
> BEGIN
>    Stat := $QIOW(,TermChannel,113,,,,Ch,1);
>    Key := Ord(Ch);
>    ReadKey := Stat;
> END; { FUNCTION ReadKey }
> 
> END. { MODULE Read_Key }
> ----- END OF READKEY.PAS ------------------------------------------------------

You should always provide an I/O status block (IOSB) for QIO operations, and
check both the system call status return and the status code in the IOSB 
for success. Also, I would use the symbolic value for the function code --
these values are defined in STARLET.PEN. Here is my version of ReadKey:

 [GLOBAL] FUNCTION ReadKey(VAR Key: Integer): Unsigned;
 
 { This function reads a single keystroke from the keyboard and returns the
   ASCII code of the key which was pressed. }
{ Note that if the QIO operation fails, the value returned to
Key is undefined. } 

 TYPE
       IOSB = RECORD
               code: [WORD] 0..65535;
               count: [WORD] 0..65535;
               info: unsigned;
             END;

 VAR   Ch:   Char;
       Stat: Unsigned;
       stat_block: IOSB;
 
 BEGIN
    Stat := $QIOW(,TermChannel,IO$_READVBLK,stat_block,,,Ch,1);
    Key := Ord(Ch);
    IF NOT ODD(Stat) THEN
        ReadKey := Stat
    ELSE
        ReadKey = stat_block.code;
 END; { FUNCTION ReadKey }
 
 END. { MODULE Read_Key }

See Chapter 7 of Introduction of VMS Sysytem Services for details,
especially section 7.10 -- I/O Completion Status.

> Ron Pacheco  "puh-check'-oh"  8-)              NET Mail: ronp@cs.umr.edu

George Merriman, Cambridge Computer Associates