How to find the max value of unknown integer type

Question

How can I find the maximal integer value of an unknown type? Is there something more efficient than this:

template<class T>
T test(T i) {
    if (((T)-1) > 0)
       return -1;
    T max_neg = ~(1 << ((sizeof(T)*8)-1));
    T all_ones = -1;
    T max_pos = all_ones & max_neg;
    return max_pos;
}

Answer 1

Use std::numeric_limits<T>::max(). Since C++11, this function is constexpr and thus evaluated at compile-time.

Answer 2

std::numeric_limits<T>::max() is a good starting point.