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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).