[C++]怎样将C++对象分配在堆/栈上

相信一些朋友也碰见过这样的面试题目,本文尝试着给出解答.

1. 分配对象在堆上

　　那么,必然要禁止对象在栈上面分配.一个很简单的办法,就是构造函数私有化(提供额外的接口生成对象),那么在栈上面就不可以分配.可是我们还需要这个对象要被析构,那么可以提供一个接口,显式的释放掉这个接口,也就是说delete也得给他禁掉~~~

　　考虑另外一个问题,C++有placement new,我自己new一块内存,然后在你这上面构造.问题就变得很恶心,看来我们只有把new,delete都给他禁掉...

　　好了,我们现在知道该怎么做:

• createInstance()接口产生对象
• dispose()接口销毁对象
• new/delete操作符全部不可见

来看我们的代码:

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. 分配对象在栈上

　　只能分配对象在栈上面,那么new显然是不能用的,否则就是在堆上面分配对象了,理所当然,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();
};

比较需要注意的地方是,new/delete有多个重载,算上[]的话,就是3*2*2=12个操作符.....