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Effective C++: ??????C++?????

Effective C++??C++???????????????????????????????????C++??????????????????????????????????????

1. ???????

?C++??????? deallocation ??????????????????????????????????????????????????????????????????????????????????

???? std::new_handler ??????????????? deallocation ?????????????????

class NewHandlerHolder {public:    explicit NewHandlerHolder(std::new_handler nh)        : handler(nh) {}    ~NewHandlerHolder() {        std::set_new_handler(handler);    }private:    std::new_handler handler;    NewHandlerHolder(const NewHandlerHolder& other);    NewHandlerHolder& operator=(const NewHandlerHolder& other);};

??? NewHandlerHolder ????????????????????

2. ?????????

????????????????????????????????????????????

template
   
    class NewHandlerSupport {public:    static std::new_handler set_new_handler(std::new_handler p) throw();    static void* operator new(std::size_t size) throw(std::bad_alloc);    static void* operator new(std::size_t size, std::nothrow_t& nt) throw();private:    static std::new_handler currentHandler;};template
    
     std::new_handler NewHandlerSupport
     
      ::currentHandler = NULL;template
      
       std::new_handler NewHandlerSupport
       
        ::set_new_handler(std::new_handler p) throw() {    std::new_handler oldHandler = currentHandler;    currentHandler = p;    return oldHandler;}template
        
         void* NewHandlerSupport
         
          ::operator new(std::size_t size, std::nothrow_t& nt) throw() { NewHandlerHolder h(std::set_new_handler(currentHandler)); return ::operator new(size, nt);}template
          
           void* NewHandlerSupport
           
            ::operator new(std::size_t size) throw(std::bad_alloc) { NewHandlerHolder h(std::set_new_handler(currentHandler)); return ::operator new(size);}
           
          
         
        
       
      
     
    
   

??? NewHandlerSupport ???????????????????????????????

3. ?????????

???? NewHandlerSupport ??????????????????????????????????????? std::nothrow ??? crash?

template
   
    void* NewHandlerSupport
    
     ::operator new(std::size_t size, std::nothrow_t& nt) throw() {    NewHandlerHolder h(std::set_new_handler(currentHandler));    return ::operator new(size, nt);}
    
   

???????????????????? std::nothrow ????????? crash?

4. ????

????????????????????????????

class Widget : public NewHandlerSupport
   
     {public:    Widget() {}    ~Widget() {        std::cout << "Widget Destructor Enter" << std::endl;    }};
   

?? Widget ???? NewHandlerSupport<Widget>????????????? deallocation ????

???????????????

int main() {    std::cout << "Hello World!" << std::endl;    Widget::set_new_handler(NULL);    std::tr1::shared_ptr
   
     pW(new Widget);    Widget* pw2 = ::new (std::nothrow) Widget;    if (pw2) {        delete pw2;    }    return 0;}
   

???????????????????????????

5. ??

?????????????????????????????????????????Effective C++ ??????????????????????C++???

??????????????????????????