Array placement-new requires unspecified overhead in the buffer?

Question

5.3.4 [expr.new] of the C++11 Feb draft gives the example:

new(2,f) T[5] results in a call of operator new[](sizeof(T)*5+

Answer 1

Calling any version of operator new[] () won't work too well with a fixed size memory area. Essentially, it is assumed that it delegates to some real memory allocation function rather than just returning a pointer to the allocated memory. If you already have a memory arena where you want to construct an array of objects, you want to use std::uninitialized_fill() or std::uninitialized_copy() to construct the objects (or some other form of individually constructing the objects).

You might argue that this means that you have to destroy the objects in your memory arena manually as well. However, calling delete[] array on the pointer returned from the placement new won't work: it would use the non-placement version of operator delete[] ()! That is, when using placement new you need to manually destroy the object(s) and release the memory.