FreeBSD layers narrow and wide character typing on top of a single common mechanism based upon 32-bit signed "runes". Basically, the 256 narrow characters are

FreeBSD layers narrow and wide character typing on top of a single common mechanism based upon 32-bit signed "runes". Basically, the 256 narrow characters are treated as the first 256 characters in the Unicode BMP, and an accident of implementation allows one to pass in other Unicode code points to the narrow character functions, given that the int and wint_t types are designed to be trivially convertible to a "rune".