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From: wen-king@cit-vlsi.UUCP
Newsgroups: comp.unix.wizards,comp.unix.questions
Subject: Re: Tty characters 'undefined' value revisited
Message-ID: <1704@cit-vax.Caltech.Edu>
Date: Thu, 5-Feb-87 15:03:59 EST
Article-I.D.: cit-vax.1704
Posted: Thu Feb  5 15:03:59 1987
Date-Received: Sat, 7-Feb-87 14:41:46 EST
References: <152@quacky.mips.UUCP>
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Reply-To: wen-king@cit-vlsi.UUCP (Wen-King Su)
Organization: California Institute of Technology
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Xref: watmath comp.unix.wizards:847 comp.unix.questions:928

In article <152@quacky.mips.UUCP> dce@quacky.UUCP (David Elliott) writes:
>
>Basically,
>the problem is that the 4.3BSD documentation says that a value of -1
>means 'undefined', but our compilers generate unsigned characters.
>
>The general concensus of the responses I got is that the ttychars
>structure should be changed so that all of the members are shorts or
>ints instead of chars.
>
>Can anyone think of a reason NOT to do this? Are there places where
>these values are expected to be chars, and will broken by this change?

I remember vaguely that you were having problems comparing chars to
the constant -1.  The comparison:

    char c;
    c = -1;
    if(c == -1) ...

tests true on one some but false on others.  That is to be expected
because C does not specify how chars are to be casted to ints.
What you can do is to do the comparison like this:

    char c;
    c = -1;
    if(c == (char) -1) ...

This should test true on all machines.