wint_t towlower(wint_t wc);
wint_t towupper(wint_t wc);
towupper(S) converts its argument wc to the corresponding uppercase wide-character code as its return value.
The argument wc must be of type wint_t; its value must be that of a valid wide-character code in the current locale or must equal the value of WEOF. The behaviors of towlower( ) and towupper( ) are undefined if any other value is passed to them.
The case of a wide-character code is defined by character type information in the program locale category LC_CTYPE. The conversion takes place only when wc represents a valid wide character and its corresponding wide character of the opposite case exists. If wc does not have a corresponding wide character of the opposite case, it is returned without any change.
The value of errno is undefined.