The wctrans_t type represents a mapping which can map a wide character to another wide character. Its nature is implementation dependent, but the special value (wctrans_t)0 denotes an invalid mapping. Nonzero wctrans_t values can be passed to the towctrans function to actually perform the wide character mapping.
The wctrans function returns a mapping, given by its name. The set of valid names depends on the LC_CTYPE category of the current locale, but the following names are valid in all locales.