constexpr pointer/reference initialization

Question

I have an set of registers in MCU, and each of them has an unique adress. Imagine I have some register, that can be described with struct

struct RegisterDefinition{
    u32 v1;
    u32 v2;
    u32 v3;
    u32 v4;
};

I know (from MCU reference manual), the adress that one of the registers of that type has in memory

#define REGISTER_ADRESS 0x12345678

how can I constexpr initialize a pointer or reference of type RegisterDefinition, so I will be able to use that variable in constexpr constructors of other classes?

like

inline constexpr somedef* registerPointer = reinterpret_cast<somedef*>(REGISTER_ADRESS);

inline constexpr somedef* registerPointer = reinterpret_cast<somedef*>(REGISTER_ADRESS);or inline constexpr somedef& registerRef = *reinterpret_cast<somedef*>(REGISTER_ADRESS); — lazba
– lazba, Commented Oct 13, 2023 at 17:04
So you're asking how to workaround the ban on reinterpret_cast in constant expressions? — Ben Voigt
– Ben Voigt, Commented Oct 13, 2023 at 17:05
I guess, yes. It seems for my question to be similar to stackoverflow.com/a/10376574/15879231 — lazba
– lazba, Commented Oct 13, 2023 at 17:07

user17732522 · Accepted Answer · 2023-10-13 17:07:39Z

0

This is currently impossible. The language does not permit it. reinterpret_cast is not permitted in constant expressions and there is no workaround.

Store the integral value of the address in a constexpr variable instead and use e.g. a function that returns a pointer from that integral value by reinterpret_cast as late as possible in whatever calculation you want to do at compile-time.

answered Oct 13, 2023 at 17:07

user17732522

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