Constants

Constants are objects whose values cannot be changed after initialization. In C++, const makes an object read-only. This improves safety and clarity by preventing accidental modification.

const does not necessarily mean compile-time: a const object can be initialized at runtime. Use constexpr (and, for initialization-only guarantees of static storage, constinit) for compile-time contexts.

Use the const keyword for read-only objects. Use constexpr when you need a compile-time constant expression (e.g., for non-type template parameters, std::array sizes, case labels).

Key rules about constants:

const data members must be initialized by a default member initializer or in the constructor's member-initializer list.

Const with pointers can apply to the pointed-to value, the pointer itself, or both.

Use constants for values that should not change during program execution, such as: