The towupper() function has as a domain a type wint_t, the value of which must be a character representable as a wchar_t, and must be a wide-character code corresponding to a valid character in the current locale or the value of WEOF. If the argument has any other value, the argument is returned unchanged. If the argument of towupper() represents a lower-case wide-character code (as defined by character type information in the program locale category LC_CTYPE), the result is the corresponding upper-case wide-character code. All other arguments in the domain are returned unchanged.

Upon successful completion, towupper() returns the upper-case letter corresponding to the argument passed. Otherwise, it returns the argument unchanged.

No errors are defined.

See attributes(5) for descriptions of the following attributes:

iswalpha(3C), setlocale(3C), towlower(3C), attributes(5)