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From: stt@inmet.inmet.com
Newsgroups: comp.lang.ada
Subject: Re: Keyboard input
Message-ID: <20600064@inmet>
Date: 25 Sep 90 13:36:00 GMT
References: <39@screamer.csee.usf.edu>
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Nf-ID: #R:screamer.csee.usf.edu:39:inmet:20600064:000:1775
Nf-From: inmet.inmet.com!stt    Sep 25 09:36:00 1990


Re: Single-character Terminal I/O, Portability, etc.

This really has nothing to do with C vs. Ada.

This is an O/S interface issue.  If you are talking
Unix, then there is a "standard" (almost) way of
accomplishing "raw" I/O.  If you are talking about`
some other operating system, then it will certainly
be different, if possible at all.  If you are talking
Posix, there are a number of options for "non-canonical"
terminal processing, which provide essentially all of
the capabilities you would want.  There is now a proposed standard
Ada binding to these capabilities (package POSIX_Terminal_Functions).

As far as portability, you will have to survey the O/Ss of
interest, come up with an interface which you can
implement everywhere, and then implement it as appropriate.
Ultimately, I suspect there will be some assembly language
involved, either written by you or by the vendor, since
neither C nor Ada compilers will normally generate
direct O/S system calls.  Of course, if you are using Unix,
then a C library is provided which already has the necessary
interfaces.  Most compiler vendors on Unix provide a similar
library for Ada.  Ideally, they will begin to converge
on the Posix proposed standard for providing these capabilities.

In any language, if you refuse to ever go outside of the language
to interface with the O/S or external subsystems, you may end up
talking only with yourself.  In any case, it usually only takes
a few lines of Assembler or other language.  You may not notice
it in C since you don't have to announce your intentions
with a "pragma Interface" to call an assembler routine, but you
can rest assured that most C system-call libraries are implemented
in assembler by someone.

S. Tucker Taft
Intermetrics, Inc.
Cambridge, MA  02138