5.7.3.8 Signed-char Option

The -fsigned-char option forces plain char objects to have a signed type.

By default, the plain char type is equivalent to unsigned char. The -funsigned-char (or -fno-signed-char option) makes this type explicit.

The -fsigned-char (or -fno-unsigned-char option) makes it explicit that plain char types are to be treated as signed integers.

Consider explicitly stating the signedness of char objects when they are defined, rather than relying on the type assigned to a plain char type by the compiler.