iswalpha

Iswalpha is a wide-character classification function in the C standard library. It tests whether a given wide character is alphabetic according to the current locale. It is declared in the header <wctype.h> and has the signature int iswalpha(wint_t wc). The argument wc should be a value representable as wint_t (for example a wchar_t converted to wint_t); WEOF is not a valid input. The function returns a nonzero value if wc belongs to the alphabetic category (the Alpha class) of the current LC_CTYPE locale, and zero otherwise.

Locale dependence: The result depends on the program’s current locale, set via setlocale or the appropriate locale mechanisms. In the default "C" or "POSIX" locale, only ASCII letters are considered alphabetic. In other locales, letters from additional scripts may be classified as alphabetic, depending on the locale data provided by the implementation.

Relation to other functions: iswalpha is the wide-character counterpart to isalpha from <ctype.h>. On some platforms, iswalpha may be defined as a macro. Some environments provide a locale-specific variant such as iswalpha_l to select a particular locale without affecting the global locale.

Notes: Proper use requires passing a valid wide character value representable as wint_t; passing an invalid value or WEOF leads to undefined or unspecified behavior depending on the implementation. Classification relies on the underlying locale data and wide-character encoding used by the platform.