Most efficient/elegant way to clip a number?

Question

Given a real (n), a maximum value this real can be (upper), and a minimum value this real can be (lower), how can we most efficiently clip n, such that it remains between lo

Answer 1

Why rewrite something that's already been written for you?

#include 
boost::algorithm::clamp(n, lower, upper);

As of C++17, this is now part of the STL:

#include 
std::clamp(n, lower, upper);