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From: jrk@sys.uea.ac.uk (Richard Kennaway)
Newsgroups: comp.sys.mac.programmer
Subject: character codes vs. key codes
Summary: When to use charcodes, when to use keycodes?
Message-ID: <1074@sys.uea.ac.uk>
Date: 15 May 91 17:39:52 GMT
Sender: jrk@sys.uea.ac.uk
Lines: 38

When should one use key codes, and when character codes, to determine
which key was typed?

IM 1 says that one should normally use character codes, not keycodes,
but sometimes one has no alternative but to use keycodes.  For example,
on the Extended Keyboard, the function keys F1-F15 all generate the same
character code, and can only be distinguished by their keycodes.

In some cases, the answer is fairly clear.  For determining whether a key
event is a visible character, to be inserted into a piece of text, one
should use the character code.  The character codes for return and
control-M are the same, as are those for enter and control-C, so those
must be detected by key codes (unless you're writing a terminal
emulator - outside that context, the relation between control-M and
return is of only historical significance).  Identifying F1-F15
requires the key code.  Distinguishing keypad characters from main
keyboard characters requires key codes.

What should one do in the case of arrow keys?  The escape key?  (The
latter is probably ambiguous with control-[, but I havent tested this.)

The problem with using key codes is that the relation between key codes
and character codes may vary from one keyboard to another.  According
to the latest version of TN 160, an extra level of code mapping has
recently been introduced between the physical keystroke and the event
record, adding a further source of uncertainty about what the key codes
and character codes that my program sees really mean.

I can't experiment with all the different keyboards and Systems that
exist.  Are there general rules which will work in all cases?  I'm not
wanting to do anything low-level or complicated, like using the keyboard
to control a video game, just a simple text editor that correctly handles
every possible key event on all Macs, all keyboards, and all Systems.  Is
this possible?

--
Richard Kennaway          SYS, University of East Anglia, Norwich, U.K.
Internet:  jrk@sys.uea.ac.uk            uucp:  ...mcsun!ukc!uea-sys!jrk