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From: David Brown <david.brown@hesbynett.no>
Newsgroups: comp.arch
Subject: Re: 80286 protected mode
Date: Wed, 9 Oct 2024 22:22:16 +0200
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On 09/10/2024 20:10, Thomas Koenig wrote:
> David Brown <david.brown@hesbynett.no> schrieb:
> 
>> When would you ever /need/ to compare pointers to different objects?
>> For almost all C programmers, the answer is "never".
> 
> Sometimes, it is handy to encode certain conditions in pointers,
> rather than having only a valid pointer or NULL.  A compiler,
> for example, might want to store the fact that an error occurred
> while parsing a subexpression as a special pointer constant.
> 
> Compilers often have the unfair advantage, though, that they can
> rely on what application programmers cannot, their implementation
> details.  (Some do not, such as f2c).

Standard library authors have the same superpowers, so that they can 
implement an efficient memmove() even though a pure standard C 
programmer cannot (other than by simply calling the standard library 
memmove() function!).