cast any pointer to char poiner using static_cast

Question

If according to strict aliasing rule char pointer may point to any type pointer, then why can't I cast any-type pointer to char pointer using static_cast?

char *ptr;
int *intPtr;

ptr = reinterpret_cast<char*>(intPtr); // ok
ptr = static_cast<char*>(intPtr); // error: invalid static_cast from type 'int*' to type 'char*'

Answer 1

How static_cast works is unrelated to the strict aliasing rule.

static_cast will not allow you to cast between arbitrary pointer types, it can only be used to cast to¹ and from²void* (and casting to void* is usually superfluous as the conversion is already implicit³).

You could do this

ptr = static_cast<char*>(static_cast<void*>(intPtr));

but there is absolutely no difference⁴ between that and

ptr = reinterpret_cast<char*>(intPtr);

---

https://github.com/cplusplus/draft/blob/master/papers/n4140.pdf

¹[expr.static.cast] / 6

²[expr.static.cast] / 13

³[conv.ptr] / 2

⁴[expr.reinterpret.cast] / 7