class X{
public:

    explicit X(int n): n_(n){
    }

    void * operator new(std::size_t){
        return std::allocator<X>().allocate(1, static_cast<X*>(0));
    }

    void operator delete(void * p){
        std::allocator<X>().deallocate(static_cast<X*>(p), 1);
    }

private:

    X(X const &);
    X & operator=(X const &);

    int n_;
};

class Y{
public:

    explicit Y(int n): n_(n){
    }

    void * operator new(std::size_t n){
        return boost::detail::quick_allocator<Y>::alloc(n);
    }

    void operator delete(void * p, std::size_t n){
        boost::detail::quick_allocator<Y>::dealloc(p, n);
    }

private:

    Y(Y const &);
    Y & operator=(Y const &);

    int n_;
};

for Codegear: alignof(T)
for GCC: __alignof__(T)
for MSC: __alignof(T)

Y y_v = new Y(1);