const和constexpr指针之间的区别

Question

What is the difference between the following two pointer definitions

int i = 0;
const int *p = &i;
constexpr int *cp = &i;

Answer 1

const int *p = &i; means:

• p is non-const: it can be reassigned to point to a different int
• i cannot be modified through p without use of a cast

constexpr int *cp = &i; means:

• cp is const : it cannot be reassigned
• i can be modified through p

In both cases, p is an address constant if and only if i has static storage duration. However, adding constexpr will cause a compilation error if applied to something that is not an address constant.

To put that another way: constexpr int *cp = &i; and int *const cp = &i; are very similar; the only difference is that the first one will fail to compile if cp would not be an address constant.