Does ctype.h still require unsigned char?

Question

Traditionally, it was - strictly speaking - an error to pass a signed char to the ctype.h predicates because they were only defined for -1 to 255, so -128 to -2 could end up in reading outside array bounds.

Was this ever fixed, or do you still strictly speaking have to use unsigned char to avoid undefined behaviour in modern versions of C?

Letsou

Modern programs have only increasing chances to be confronted to characters in the range 128-255, which would be misinterpreted as negative if seen as signed chars, so the answer is “more than ever”. – Priestley

Answer 1

do you still strictly speaking have to use unsigned char to avoid undefined behavior in modern versions of C?

Yes, from the C11 draft standard section 7.4 Character handling <ctype.h> paragraph 1 says (emphasis mine):

The header declares several functions useful for classifying and mapping characters.¹⁹⁸⁾ In all cases the argument is an int, the value of which shall be representable as an unsigned char or shall equal the value of the macro EOF. If the argument has any other value, the behavior is undefined.

This also holds for draft C99 standard as well, you can find it in the same section.

Uranian