C++11 recursive constexpr static string length and compare

const_str_funcs.hpp

constexpr bool is_str_end(const char *t) {
    return !(t) || !(*t);
}

constexpr int recursive_cstr_len(const char * t) {
    return is_str_end(t) ?
        0 :
        1 + recursive_cstr_len(t + 1);
}

constexpr int str_equal = 0;
constexpr int str_greater = 1;
constexpr int str_lesser = -1;

constexpr int recursive_cstr_cmp(const char *a, const char *b) {
    return is_str_end(a) ?
        ( is_str_end(b) ? str_equal : str_lesser) :
        (
            (*a != *b) ?
            ( *a > *b ? str_greater : str_lesser) :
            recursive_cstr_cmp(a+1,b+1)
        );
}