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From: defaria@hpcupt3.cup.hp.com (Andy DeFaria)
Newsgroups: comp.lang.pascal
Subject: Re: Re: CTRL-Characters
Message-ID: <45670004@hpcupt3.cup.hp.com>
Date: 1 Apr 91 17:56:01 GMT
References: <1991Mar28.005803.25890@oz.plymouth.edu>
Organization: Hewlett Packard, Cupertino
Lines: 79

>/ hpcupt3:comp.lang.pascal / einstein@cs.mcgill.ca (Michael CHOWET) / 12:18 am  Mar 30, 1991 /
>In article <1991Mar27.161213.2100@cs.mcgill.ca> storm@cs.mcgill.ca 
>(Marc WANDSCHNEIDER) writes:
>
>>How do I make a PASCAL program recognize CTRL characters (or ALT characters 
>>for that matter).  Ie I want the following:
>
>>     IF CH = CTRL-G then 
>>          BEGIN 
>>           blahblahb
>>	  END;
>
>  Actually, there are two ways to get at this. If you feel like dragging out
>the list of ASCII codes, you can type:
>
>  If CH = #07 Then DoSomething ; 
>
>  Basically, the # symbol followed by the ASCII code. Simple enough, right?
>
>  But if you want the actual character in there, hit the ^P. The following
>character (your CTRL-char) will be accepted as a literal, ie it will be
>inserted into the text without trying to process it as an editor control key.

IMHO this is asking for trouble and curses from fellow programmers.  What I do
is:

Unit ASCII;

Interface

Const
   ControlA    = #01;
   ControlB    = #02;

   ...

   ControlG    = #07;

Implementation

End. { ASCII }

Program Foo;

Uses ASCII;

Var
   Character : Char;

Begin { Foo }
   Character := ReadKey;

   If Character = ControlG then
      { Do want you want }
   else
      { Do something else }

End. { Foo }

If you define all ASCII characters in the Unit ASCII then you can easily
refer to them *symbolically* by simply including the ASCII unit in your uses
statement.

Note that Control characters do NOT have a scan code.  Function keys, and all
there derivitives like ControlF1, AltF2, etc, do.  What I have done is wrote a
more generic GETKEY function that handles these things and returns things like
ControlF1 or AltF2, which I have defined in the ASCII unit as something like:

Const
   ControlF1 = #170;
   ControlF2 = #171;
   ...

   AltF1     = #180;
   AltF2     = #181;

I'm pretty sure that the characters #170 on up aren't used (although they are
probably 8-bit characters used for other language sets but I'm not concerned
with them).