The placement-new operator constructs an object on a pre-allocated buffer. The pre-allocated buffer has to be allocated on the heap.
char *pbuff = new char[1024]; // heap allocation using plain new
Person *p = new (pbuff) Person; // placement new uses a pre-allocated buffer
You may be tempted to use a buffer allocated on the stack to avoid the need of explicitly freeing it:
char pbuff [1024]; //bad idea: stack allocation instead of heap
Person *p = new ( pbuff ) Person; //undefined behavior
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