towlower

Towlower is a function in the C standard library used to convert a wide character to its lowercase equivalent. It operates on wide characters and is part of the wctype.h header, with related wide-character utilities commonly used alongside wchar.h for working with wchar_t strings. The function name is towlower, though some texts may spell it informally as towlower.

Prototype and behavior: The function is declared as int towlower(int wc). It takes a wide character value (promoted to int, typically representing a wint_t) and returns the lowercase mapping of that character according to the current locale. If there is no lowercase mapping for the input, or if the input does not have a lowercase form, towlower returns the input value unchanged. The conversion is locale-dependent and follows the rules of the program’s LC_CTYPE category.

Locale and portability: The results produced by towlower depend on the program’s current locale, which is set with setlocale. Some implementations provide a locale-specific variant, such as towlower_l, to apply a particular locale directly. Towlower is specified by the C standard and is widely supported across major compilers and standard libraries, including GCC, Clang, and MSVC.

Usage notes: Towlower is used when processing wide-character strings (for example, wchar_t arrays) or Unicode code points in environments that represent characters as wide types. It is not designed for multibyte encodings like UTF-8 directly. For narrow-character text, the corresponding function is tolower from ctype.h; for wide characters, towlower is the appropriate counterpart.

See also: tolower, towupper, setlocale, wctype.h, wchar.h.