Modern C++ Programming Cookbook

How it works...

The const keyword is used for declaring variables as constant at runtime; this means that, once initialized, they cannot be changed. However, evaluating the constant expression may still imply runtime computation. The constexpr keyword is used for declaring variables that are constant at compile time or functions that can be executed at compile time. constexpr functions and objects can replace macros and hardcoded literals without any performance penalty.

Declaring a function as constexpr does not mean that it is always evaluated at compile time. It only enables the use of the function in expressions that are evaluated during compile time. This only happens if all the input values of the function can be evaluated at compile ...