C++ Primer, Fifth Edition

19.1.2. Placement new Expressions

Although the operator new and operator delete functions are intended to be used by new expressions, they are ordinary functions in the library. As a result, ordinary code can call these functions directly.

In earlier versions of the language—before the allocator (§ 12.2.2, p. 481) class was part of the library—applications that wanted to separate allocation from initialization did so by calling operator new and operator delete. These functions behave analogously to the allocate and deallocate members of allocator. Like those members, operator new and operator delete functions allocate and deallocate memory but do not construct or destroy objects.

Differently from an allocator, there is no construct function we ...