条款8：写operator new和operator delete时要遵循常规

1. 首先我被一个问题所困恼：条款7中的operator new是这么写的，但条款8中的new却多了一个while。回头再仔细看下条款7，原来条款7中的operator new只处理了第一次分配内存失败的异常。

//条款7中的operator newtemplate<class T>  void* NewHandlerSupport<T>::operator new(size_t size)  {      void* memory = NULL;      new_handler old_handler = ::set_new_handler(current_handler);        try      {          memory = ::operator new(size);      }      catch (std::bad_alloc&)      {          set_new_handler(old_handler);          throw;      }        set_new_handler(old_handler);      return memory;  }  

 2. operator new要遵循哪些常规：a）要有正确的返回值. b）内存不够异常处理. c）处理请求0字节内存分配. d）避免隐藏标准new. e) 非类成员的operator new 和类成员的operator new区别. 其看起来会像下面这样：

//条款8中非类成员的operator newvoid* operator new(size_t size){if(0 == size){size = 1;}while(1){new_handler handler = NULL;void* memory = NULL;handler = set_new_handler(NULL);set_new_handler(handler);memory = ::operator new(size);if(NULL != memory)return memory;if(handler) (*handler)();else throw std::bad_alloc();}}

//条款8中类成员的operator newclass X{public:    static void* operator new(size_t size);    //...private:    //...};void* X::operator new(size_t size){    if(size != sizeof(X)) //如果X的子类的size大于sizeof(X)        return ::operator new(size);    /*if(0 == size)    {        size = 1;    }*/    while(1)    {        new_handler handler = NULL;        void* memory = NULL;        handler = set_new_handler(NULL);        set_new_handler(handler);        memory = ::operator new(size);        if(NULL != memory)            return memory;        if(handler)             (*handler)();        else             throw std::bad_alloc();    }} 
 
3. operator delete要遵循哪些常规：a）C++保证删除空指针永远是安全的，意味着我们只需要保证我们的指针不是野指针就无大碍. b）同样的非类成员的operator delete和类成员的operator delete有区别.
//非类成员的operator deletevoid operator delete(void* memory){    if(NULL == memory)        return;        ::operator delete(memory);    return;}//类成员的operator deleteclass X{public:static void* operator new(size_t size);static void operator delete(void* memory, size_t size);//...private://...};void X::operator delete(void* memory, size_t size){if(NULL == memory)return;if(size != sizeof(X))//如果X的子类的size大于sizeof(X){::operator delete(memory);//标准的deletereturn;}//自定义的delete，这里也调用标准的delete::operator delete(memory);}


	
				
	
					   
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