iswlower

iswlower is a function in the C standard library used to test whether a wide character is a lowercase letter. It is declared in the header wctype.h and is the wide-character counterpart to the islower function. The classification is locale-dependent, relying on the current LC_CTYPE setting.

The function signature is int iswlower(wint_t wc); it takes a wide character value represented as a wint_t and returns a nonzero value if wc is a lowercase wide character, and zero otherwise. The exact nonzero value is implementation-defined. In the default C locale or in ASCII environments, iswlower typically returns nonzero only for the characters 'a' through 'z'. In other locales, additional characters from non-Latin scripts may be classified as lowercase.

Behavior and usage considerations: iswlower classifies characters according to the current locale, so changing the locale with setlocale may alter results. It operates on wide characters, so inputs are usually obtained from wide-character input or by using related functions such as towlower or towupper. If the input is not a valid wide character within the current locale, the behavior is defined by the implementation and locale rules, and some implementations may treat such values as non-lowercase.

Compatibility and portability: iswlower is part of the C standard library and is available on conforming implementations that support wide characters. Portable code should include <wctype.h>, use wint_t for the argument type, and be aware of locale-related effects when comparing or filtering wide-character data.

See also: isupper, islower, iswalpha, towlower, wctype, setlocale.