ctype::do_is

virtual bool do_is(mask msk, E ch) const;
virtual const E *do_is(const E *first, const E *last,
    mask *dst) const;

The first protected member template function returns true if table[(unsigned char)(char)ch] & msk is nonzero, where table is the stored pointer to the ctype mask table.

The second protected member template function stores in dst[I] the value table[(unsigned char)(char)first[I]] & msk, where I ranges over the interval [0, last - first).