Effective C++ 条款 52：写了placement new也要写placement delete - c++编程基础

lass内声明任何operator news，它会遮掩上述这些标准形式。除非你的意思就是要阻止class的客户使用这些形式，否则确保他们在你生成的任何定制型operator new之外还可用。

解决所有问题的一个简单的做法是，建立一个base class，内含所有正常形式的new和delete：

class StandardNewDeleteForms{ 
public: 
    //normal new/delete 
    static void* operator new(std::size_t size)throw(std::bad_alloc) 
    {return ::operator new(size);} 
    static void operator delete(void* pMemory) throw() 
    {::operator delete(pMemory);} 
    //placement new/delete 
    static void*  operator new(std::size_t size, void* ptr) throw() 
    {return ::operator new(size, ptr);} 
    static void operator delete(void* pMemory, void* ptr)throw() 
    {return ::operator delete(pMemory, ptr);} 
    //nothrow new/delete 
    static void* operator new(std::size_t size, const std::nothrow_t& nt)throw() 
    {return ::operator new(size, nt);} 
    static void operator delete(void* pMemory, const std::nothrow_t&) throw() 
    {::operator delete(pMemory);} 
};

凡是想自定义形式扩充标准形式的客户，可利用继承机制及using声明式取得标准形式：

class Widget: public StandardNewDeleteForms{ 
public: 
    using StandardNewDeleteForms::operator new; 
    using StandardNewDeleteForms::operator delete; 
    static void* operator new(std::size_t size, std::ostream& logStream)throw(std::bad_alloc); 
    static void operator delete(void* pMemory, std::ostream& logStream) throw(); 
};

请记住：

（1）当你写一个placement operator new,请确定也写出了对应的placement operator delete.如果没有这样做。你的程序可能会发生隐微而时断时续的内存泄漏.
（2）当你声明placement new和placement delete。请确定不要无意识地遮掩它们的正常版本.

Effective C++ 条款 52：写了placement new也要写placement delete(二)