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From: James.Kanze@dresdner-bank.com
Newsgroups: comp.std.c++,comp.std.c
Subject: Re: C and C++ Standard incompatibility for signed character type
Date: Wed,  1 Nov 2000 16:44:48 GMT
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In article <c5vCyUAGAq$5EwFI@ntlworld.com>,
  Francis Glassborow <francisG@robinton.demon.co.uk> wrote:
> In article <slrn8vs450.igr.Team-Rocket@nightrunner.nm.dnsalias.net>,
> Niklas Matthies <Team-Rocket@gmx.net> writes
> >On Mon, 30 Oct 2000 23:51:03 GMT, Francis Glassborow
<francis.glassborow@ntlworld.com> wrote:
> >> In article
<slrn8vrl3c.uu1.Team-Rocket@nightrunner.nm.dnsalias.net>,
> >> Niklas Matthies <Team-Rocket@gmx.net> writes
> >> >It's not (in C). The uninitialized chars may have trap values
> >> >(for the type char)

> >> Please quote text to support this claim

> >It's the other way round. The standard does not specify such a
> >guarantee (unless I missed something), therefore there is none.

> The C standard requires that unsigned char has no trap values (that
> can be deduced from the rules for type punning etc.) It also
> requires that char can be exactly accessed as an unsigned char
> though the negative values will be mapped to positive values beyond
> the maximum value for char (assuming it is a signed version). I do
> not see how these requirements can allow for the existence of trap
> values.

And I don't see what is to prevent them.  Again, take Clive's example:

    CHAR_BIT == 10
    UCHAR_MAX == 1023
    CHAR_MAX == 255
    CHAR_MIN == -256

This obviously allows trapping values for char.  It also easily meets
the requirements you give.

--
James Kanze                               mailto:kanze@gabi-soft.de
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