memory management 2

class B {public:virtual ~B();void operator delete  (void*, size_t) throw();void operator delete[](void*, size_t) throw();void f(void*, size_t) throw();};class D : public B{public:void operator delete  (void*) throw();void operator delete[](void*) throw();};// Why do B's operators delete have a second parameter, whereas D's do not?// should provide new() and new[] ().// Always explicitly declare operator new() and operator delete() as static functions. They are never nonstatic member functions.// 1.D* pd1 = new D; delete pd1;  B* pb1 = new D;delete pb1;D* pd2 = new D[10];delete[] pd2;B* pb2 = new D[10];delete[] pb2;// Never treat arrays polymorphically.// 2.typedef void (B::*PMF)(void*, size_t); PMF p1 = &B::f;  // finePMF p2 = &B::operator delete; // error, because static function.// 3.class X {public:void* operator new( size_t s, int ) throw( bad_alloc ){return ::operator new( s );}}; // this invites a memory leak. because it lost operator delete.class SharedMemory{public:static void* Allocate( size_t s ){return OsSpecificSharedMemAllocation( s );}static void  Deallocate( void* p, int i = 0 ){OsSpecificSharedMemDeallocation( p, i );    }};class Y{public:   void* operator new( size_t s,SharedMemory& m ) throw( bad_alloc )    {return m.Allocate( s );    }    void  operator delete( void* p,SharedMemory& m, int i ) throw()    {m.Deallocate( p, i );    }//This Y::operator delete() is useless because it can never be called.};// think about the flowing.SharedMemory shared; ...new (shared) Y; // if Y::Y() throws, memory is leaked// the replacement global operator delete() is going to delete memory allocated normally by the default ::operator new(), // not by SharedMemory::Allocate().void operator delete( void* p ) throw(){    SharedMemory::Deallocate( p );}void operator delete( void* p,std::nothrow_t& ) throw()  {    SharedMemory::Deallocate( p );}