35. Placement New

Question.5

A developer re-initializes a UART driver at a new baud rate without allocating new memory:

alignas(UART) uint8_t buf[sizeof(UART)];
UART* u = new (buf) UART(9600);
// ... use UART at 9600 ...
u->~UART();  // Destroy old
u = new (buf) UART(115200);  // Reconstruct

Is this pattern valid?

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Select Answer

No -- you cannot construct twice in the same memory
Yes -- destroy first, then reconstruct; the buffer is reused safely
Yes -- but only if UART has no virtual functions
No -- the second new allocates from the heap