Linus Torvalds wrote:

So Morten is right - if you have a "char *", it should not be dereferenced 
and used directly, although I think glibc does the right thing (and, in 
fact, I can't understand why the standards haven't been updated to do the 
right thing: it's _not_ that hard. In fact, it should be trivial apart 
from the special case of "255" that looks undistinguishable from EOF in 
signed char representation).

Because of the special case of 255 which looks indistinguishable from 
EOF, therefore making it required?

The original mistake, of course, was allowing EOF to be passed to the 
various isxxx() macros.

	-hpa