The argument to most of the functions from <ctype.h> "shall either be
representable as an 'unsigned char' or shall equal the value of the
macro EOF".
When confronted with the infamous warning 'array subscript has type
char', there are enough programmers who don't know the background of
that warning and thus fix it in a wrong way. Neither GCC nor Clang
explain its warning to target these programmers.
Both GCC and Clang warn about 'array subscript has type char', but they
ignore the other requirements of the <ctype.h> functions, even though
these are in the C standard library.
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94182https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95177https://stackoverflow.com/a/60696378
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