What is this weird constructory syntax
The Microsoft Visual C++ compiler supports this weird thing:
// assume a class C has been defined C* p = (C*)malloc(sizeof(C)); p->C::C(); // huh?
This weird syntax is how people in olden times explicitly invoked a constructor on an uninitialized block of memory.
Then placement new arrived on the scene and made the above syntax obsolete.
// new hotness C* p = (C*)malloc(sizeof(C)); new(p) C();
But the Microsoft Visual C++ compiler still supports the old syntax for backward compatibility purposes.
Note that the corresponding explicit destructor syntax
p->C::~C(); // can be shortened to p->~C() if p is of type C*
is still standard as of this writing.