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Reading thru https://github.com/isocpp/CppCoreGuidelines/issues/1517 I got the idea to get rid of the non-constexpr reinterpret_cast from my µC code (e.g. C could be a µC internal peripheral on address 0x100). Therefore I tried std::bit_cast-ing to a pointer type.

struct C {
    inline static constexpr uintptr_t address = 0x100;
    inline static constexpr C* ptr1 = std::bit_cast<C*>(address);
    inline static /*constexpr*/ C* ptr2 = reinterpret_cast<C*>(address);
};

But according to the standard this is not possible because in this case std::bit_cast is not allowed to be constexpr (like reinterpret_cast).

Looks like this is still not possible? But why?

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  • These are the answers you might seek: en.cppreference.com/w/cpp/numeric/bit_cast#Notes en.cppreference.com/w/cpp/language/… Mainly due to the possibility of Undefined Behavior. It is marked constexpr but the implementation wouldn't able to evaluate it to a constant. Commented Oct 31, 2022 at 16:40
  • 1
    std::bit_cast with pointer types is exactly the same as reinterpret_cast, so the rules for why that isn't allowed in a constant expression are the same reasons why you can't use bit_cast. Commented Oct 31, 2022 at 16:41
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