The type ctype_base provides for const enumerations.
namespace std { class ctype_base { public: enum mask { alpha = 0x0001, blank = 0x0002, cntrl = 0x0004, digit = 0x0008, graph = 0x0010, lower = 0x0020, print = 0x0040, punct = 0x0080, space = 0x0100, upper = 0x0200, xdigit = 0x0400, alnum = alpha | digit }; }; }