On Sat, Jul 26, 2025 at 10:54 PM Jonathan Wakely wrote:
>
> Any value written to a non-static data member by the destructor is a
> dead store, it cannot be read after the destructor finishes. It is irrelevant
> whether the object was initialized using placement new.
>
> As it's a dead store, the compiler can remove that store completely.


Are you saying that the following program has undefined behaviour or
that it's not guaranteed to print "deadbeef"?

    https://godbolt.org/z/6bcnz95Ed

Specifically, are you saying that after the MyClass destructor has
returned, that the first 8 bytes of 'buf' cannot be perused?

And here it is copy-pasted:

    char unsigned buf[64u];

    struct MyClass {
        int *p = new int;
        ~MyClass(void)
        {
            delete p;
            p = (int*)(void*)0xdeadbeef;
        }
    };

    #include <iostream>
    #include <iomanip>
    using std::cout, std::hex, std::endl;

    int main(void)
    {
        MyClass *const ptr = static_cast<MyClass*>(static_cast<void*>(&buf));
        ::new(ptr) MyClass;
        ptr->~MyClass();
        // The loop on the next line is for Little Endian CPU's
        for ( unsigned i = 3u; i <= 3u; --i ) cout << hex << (unsigned)buf[i];
        cout << endl;
    }