Help with a c++ statement

The following statement is from WebKit. I am not 100% sure what it mea开发者_运维问答ns. Any clues?

new ((void*)&nullAtom) AtomicString;

It's a placement-new. It means that the AtomicString object will be constructed at the memory location pointed to inside the parentheses (&nullAtom), rather than the usual behavior (constructed on top of a bit of memory taken off of the heap).

That's a "placement new".