C++ 智能指针 　 　 　　

C++智能指针

what

是个对象,不是数据类型,对象里有个普通指针和内存被引用个数 std::auto_ptr
boost::scoped_ptr
boost::shared_ptr
boost::scoped_array
boost::shared_array
boost::weak_ptr
boost:: intrusive_ptr

why

普通指针缺点:
普通指针指向的内存需要手动delete

  1. 内存被多次delete导致程序crash
  2. 内存没被delete导致内存泄露

how

实现

class ptr
{
	friend class smart_pointer;
	int count;
	int* pointer;
};
class smart_pointer
{
public:
	smart_pointer(arguments);
	~smart_pointer();
	//含参数构造函数
	smart_pointer(int* p)
	{
		pointer = p;
		pointer.count = 1;
	}
	smart_pointer()
	{
		pointer.pointer = NULL;
		pointer.count = 0;
	}
	//赋值操作
	smart_pointer& operator=(smart_pointer& p)
	{
		p.pointer.count ++;
		if(pointer.count)
		{
			pointer.count --;
			if(pointer.count == 0)
			{
				delete pointer.pointer;
				pointer.pointer = NULL;
			}
		}
		pointer.pointer = p.pointer;
		pointer.count = p.count;
		return *this;
	}
	//拷贝构造函数
	smart_pointer(smart_pointer& p)
	{
		pointer.pointer = p.pointer;
		pointer.count = p.count;
	}
private:
	ptr pointer;
	/* data */
}; ### boost::shared_ptr  boost智能指针的引用计数也是个类，count赋值操作如下  

shared_count & operator= (shared_count const & r) // nothrow
{
    sp_counted_base * tmp = r.pi_;

    if( tmp != pi_ )
    {
        if( tmp != 0 ) tmp->add_ref_copy();
        if( pi_ != 0 ) pi_->release();
        pi_ = tmp;
    }

    return *this;
}