bug#8545: issues with recent doprnt-related changes

[Richard Stallman <rms@gnu.org>]

    No, format_end is already pointing after the object;
    the object's size is format_end - format.  So
    format_end + 1 might not be a valid pointer.

20 years ago,, Emacs allocated an extra byte with a null character
after the end of every string or buffer.  If that is still true
then this pointer actually is valid.

But it doesn't matter anyway, for reasons described below.

    Yes.  A portable C program is not allowed to create a pointer that
    doesn't point to an object,

Our C programs are allowed to create any sort of pointer we want them
to.  ISO has no authority over us.  We are concerned with standards
insofar as they matter in practice for the convenience and reliability
of our software.

Thus, the question that matters to us is whether a construct is going
to cause a problem on the plausibke platforms we will want to support.
That does not include all theoretical ISO C implementations.

    Yes.  To take an extreme example, some architectures can compute
    a pointer only by using a special pointer register, and the register's
    contents are always checked for validity, even if you don't dereference the
    pointer.

They are outside GNU's design range of targets.

    If you assign i = INT_MAX + 1, the resulting behavior is undefined.

The result is INT_MIN.  We don't try to support any theoretical machine
where this would not be so.

-- 
Dr Richard Stallman
President, Free Software Foundation
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