Standard C++ Library Reference ISO/IEC (VERSION3)

LC_CTYPE category of the current locale does not define a mapping whose name matches the
property string property, the function returns zero. Otherwise, it returns a nonzero value
suitable for use as the second argument to a subsequent call to towctrans.
The following pairs of calls have the same behavior in all locales (but an implementation can
define additional mappings even in the "C" locale):
towlower(c) same as towctrans(c, wctrans("tolower"))
towupper(c) same as towctrans(c, wctrans("toupper"))
wctrans_t
typedef s_type wctrans_t;
The type is the scalar type s-type that can represent locale-specific character mappings, as
specified by the return value of wctrans.
wctype
wctype_t wctype(const char *property);
wctrans_t wctrans(const char *property);
The function determines a classification rule for wide-character codes. If the LC_CTYPE
category of the current locale does not define a classification rule whose name matches the
property string property, the function returns zero. Otherwise, it returns a nonzero value
suitable for use as the second argument to a subsequent call to towctrans.
The following pairs of calls have the same behavior in all locales (but an implementation can
define additional classification rules even in the "C" locale):
iswalnum(c) same as iswctype(c, wctype("alnum"))
iswalpha(c) same as iswctype(c, wctype("alpha"))
iswcntrl(c) same as iswctype(c, wctype("cntrl"))
iswdigit(c) same as iswctype(c, wctype("digit"))
iswgraph(c) same as iswctype(c, wctype("graph"))
iswlower(c) same as iswctype(c, wctype("lower"))
iswprint(c) same as iswctype(c, wctype("print"))
iswpunct(c) same as iswctype(c, wctype("punct"))
iswspace(c) same as iswctype(c, wctype("space"))
iswupper(c) same as iswctype(c, wctype("upper"))
iswxdigit(c) same as iswctype(c, wctype("xdigit"))