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From: firth@sei.cmu.edu (Robert Firth)
Newsgroups: comp.arch
Subject: Re: Endian wars
Message-ID: <8496@aw.sei.cmu.edu>
Date: 9 Feb 89 13:13:35 GMT
References: <6133@columbia.edu> <3300050@m.cs.uiuc.edu> <8480@aw.sei.cmu.edu> <24384@amdcad.AMD.COM>
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In article <8480@aw.sei.cmu.edu> firth@bd.sei.cmu.edu (Robert Firth) writes:

| Could someone inform me whether the current C standard has fixed this?
| The simplest answer I guess is to rule that the address of array[upb+1]
| must always be legal; in practice this means the implementation has to
| leave dead space at the end of each memory segment.

In article <24384@amdcad.AMD.COM> tim@amd.com (Tim Olson) writes:

>That is exactly what is done in the current proposed ANSI C standard;
>the address is legal to compute, although dereferencing the address is
>undefined.  Only a single byte of "dead space" is required for this.

Thanks, Tim, and others who mailed me.  There is a copy of the latest
ANSI C in this building, but it seems to have wandered off, so I can't
look this up for myself readily.

However, is only a single byte required?  Suppose you have an array of
a struct; is it legal to compute the address of array[upb+1].component?
If so, then you really do need to allocate a complete dead array element.