[C++]怎樣將C++對象分配在堆/棧上

相信一些朋友也碰見過這樣的面試題目,本文嘗試著給出解答.

1. 指派至在堆上

　　那麼,必然要禁止對象在棧上面分配.一個很簡單的辦法,就是建構函式私人化(提供額外的介面產生對象),那麼在棧上面就不可以分配.可是我們還需要這個對象要被析構,那麼可以提供一個介面,顯式的釋放掉這個介面,也就是說delete也得給他禁掉~~~

　　考慮另外一個問題,C++有placement new,我自己new一塊記憶體,然後在你這上面構造.問題就變得很噁心,看來我們只有把new,delete都給他禁掉...

　　好了,我們現在知道該怎麼做:

• createInstance()介面產生對象
• dispose()介面銷毀對象
• new/delete操作符全部不可見

來看我們的代碼:

class HeapObject{public:static HeapObject* createInstance(){return new HeapObject;}void dispose(){delete this;}protected:HeapObject(){}~HeapObject(){}static void* operator new (std::size_t size) throw (std::bad_alloc){return ::operator new(size);}static void* operator new (std::size_t size, const std::nothrow_t& nothrow_constant) throw();static void* operator new (std::size_t size, void* ptr) throw();static void* operator new[] (std::size_t size) throw (std::bad_alloc);static void* operator new[] (std::size_t size, const std::nothrow_t& nothrow_constant) throw();static void* operator new[] (std::size_t size, void* ptr) throw();static void operator delete (void* ptr) throw (){::operator delete(ptr);}static void operator delete (void* ptr, const std::nothrow_t& nothrow_constant) throw();static void operator delete (void* ptr, void* voidptr2) throw();static void operator delete[] (void* ptr) throw ();static void operator delete[] (void* ptr, const std::nothrow_t& nothrow_constant) throw();static void operator delete[] (void* ptr, void* voidptr2) throw();};

2. 指派至在棧上

　　只能指派至在棧上面,那麼new顯然是不能用的,否則就是在堆上面指派至了,理所當然,delete也得禁掉.

class StackObject{public:StackObject(){}~StackObject(){}protected:static void* operator new (std::size_t size) throw (std::bad_alloc);static void* operator new (std::size_t size, const std::nothrow_t& nothrow_constant) throw();static void* operator new (std::size_t size, void* ptr) throw();static void* operator new[] (std::size_t size) throw (std::bad_alloc);static void* operator new[] (std::size_t size, const std::nothrow_t& nothrow_constant) throw();static void* operator new[] (std::size_t size, void* ptr) throw();static void operator delete (void* ptr) throw ();static void operator delete (void* ptr, const std::nothrow_t& nothrow_constant) throw();static void operator delete (void* ptr, void* voidptr2) throw();static void operator delete[] (void* ptr) throw ();static void operator delete[] (void* ptr, const std::nothrow_t& nothrow_constant) throw();static void operator delete[] (void* ptr, void* voidptr2) throw();};

比較需要注意的地方是,new/delete有多個重載,算上[]的話,就是3*2*2=12個操作符.....