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From: guy%gorodish@Sun.COM (Guy Harris)
Newsgroups: comp.sources.bugs
Subject: Re: cent problems (other than register)
Message-ID: <24284@sun.uucp>
Date: Mon, 27-Jul-87 21:01:58 EDT
Article-I.D.: sun.24284
Posted: Mon Jul 27 21:01:58 1987
Date-Received: Wed, 29-Jul-87 01:51:46 EDT
References: <24033@sun.uucp> <345@rabbit1.UUCP>
Sender: news@sun.uucp
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> My system has TIONREAD defined as being usable against any file descripter
> and can be used against input as well as output. True, it may not be
> available on many UN*Xes, my version (AIX - a collection of many dialects)
> does.

It is probably not available on *most* UNIXes; it is not in V7, 4BSD,
nor S3/S5.  Most likely, it is an AIXism.

It also has a truly stupid name, if it can be used against output;
with a name like "TIONREAD", it makes sense that it can be used
against input, but unless somebody from IBM is thinking of the old
IBM 1130 printer that permitted you to "read" which character was
under the print hammers it doesn't make sense to ask how many
characters can be "read" from an output device.

Furthermore, if you have a single descriptor open for reading from
and writing to a terminal, will it tell you how many characters can
be read without blocking, or will it tell you how many characters are
queued up to be transmitted (the latter is what TIOCOUTQ tells you)?

(And if it is usable against any file descriptor, why does it begin
with "T" rather than "F"?  The "TIO" hints that it is for
terminals....)
	Guy Harris
	{ihnp4, decvax, seismo, decwrl, ...}!sun!guy
	guy@sun.com