operator new and delete

Effective C++的笔记
 1 #include <tr1/memory>
 2 #include <iostream>
 3 
 4 class NewHandlerHolder {
 5 public:
 6     explicit NewHandlerHolder(std::new_handler nh)
 7         :handler(nh){ }
 8     ~NewHandlerHolder() { std::set_new_handler(handler); }
 9 private:
10     std::new_handler handler;
11     NewHandlerHolder(const NewHandlerHolder&);
12     NewHandlerHolder & operator=(const NewHandlerHolder&);
13 };
14 
15 template <typename T>
16 class NewHandlerSupport {
17 public:
18     static std::new_handler set_new_handler(std::new_handler p) throw();
19     static void *operator new(std::size_t size) throw(std::bad_alloc);
20     static void *operator new(std::size_t size, std::nothrow_t &) throw();
21 
22 private:
23     static std::new_handler currentHandler;
24 };
25 
26 template <typename T>
27 std::new_handler NewHandlerSupport<T>::currentHandler = NULL;
28 
29 template <typename T>
30 std::new_handler 
31 NewHandlerSupport<T>::set_new_handler(std::new_handler p) throw()
32 {
33     //throw()指出，该函数不允许抛出异常，否则属于严重错误
34     std::new_handler oldHandler = currentHandler;
35     currentHandler = p;
36     return oldHandler;
37 }
38 
39 template <typename T>
40 void *
41 NewHandlerSupport<T>::operator new(std::size_t size, std::nothrow_t &nt) throw()
42 {
43     NewHandlerHolder h(std::set_new_handler(currentHandler));
44     return ::operator new(size, nt);
45 }
46 
47 template <typename T>
48 void *
49 NewHandlerSupport<T>::operator new(std::size_t size) throw(std::bad_alloc)
50 {
51     NewHandlerHolder h(std::set_new_handler(currentHandler));
52 
53     return ::operator new(size);
54 }
55 
56 class Widget : public NewHandlerSupport<Widget>{
57 public:
58     Widget(){ }
59     ~Widget(){ std::cout << "Widget Destructor Enter" << std::endl; }
60 };
61 
62 int main(void)
63 {
64     std::cout << "Hello World!" << std::endl;
65 
66     Widget::set_new_handler(NULL);
67 
68     std::tr1::shared_ptr<Widget> pW(new Widget);
69 
70     Widget *pw2 = ::new (std::nothrow) Widget;
71     if(pw2)
72         delete pw2;
73 
74     return 0;
75 }