cwctype

cwctype is a header in the C++ standard library that provides wide-character classification and mapping utilities, mirroring the C library’s ctype.h but designed for wide characters. It declares functions and types that operate on wide-character values (wchar_t and wint_t) to test character properties and perform case conversion, in a way that is intended to be compatible with the C wide-character facilities.

Key functions include iswalpha, iswupper, iswlower, iswdigit, iswxdigit, iswalnum, iswspace, iswpunct, iswgraph, iswprint, iswcntrl, and iswblank (where supported). There is also iswctype(wint_t, wctype_t) to test whether a wide character has a specified property mask. For case mapping, towlower and towupper convert wide characters to their lowercase or uppercase equivalents. The header also defines the types wint_t, wctype_t and wctrans_t, which are used with these utilities. Additional functionality related to locale-aware transformations is provided via wctrans and towctrans.

Usage is analogous to the narrow-character <ctype.h> functions, but operates on wide characters. For example, towupper(L'a') yields L'A', and iswalpha(L'A') indicates whether a wide character is alphabetic. The results of these functions are locale-sensitive; the current C locale influences their behavior on many platforms. Some environments offer additional locale-specific variants (often with a _l suffix) to select a particular locale explicitly.

In practice, cwctype complements other wide-character facilities in the standard library, such as cwchar and <locale> support, enabling portable wide-character processing in C++ programs. See also: ctype (for narrow characters), cwchar, and locale facilities.