智能指针share_ptr 简单剖析！

话不多说直接上码！

//shared_ptr的简单实现版本 基于引用记数的智能指针

namespace boost //空间库boost
{
template<class T>
class shared_ptr
{
typedef unsigned longsize_type;
private:
T *px; //指向指针
size_type* pn; //引用计数
public:
explicitshared_ptr(T* p=0) : px(p)
{
pn = new size_type(1);
}

template<typename Y>
shared_ptr(Y* py)
{
pn = newsize_type(1);
px=py;
}

shared_ptr(constshared_ptr& r) : px(r.px)
{
++*r.pn;
pn = r.pn;
}

template<typename Y>
shared_ptr(constshared_ptr<Y>& r)//用于 多态 ：一个接口多种实现方法
{
px = r.px;
++*r.pn;
pn = r.pn; //shared_count::op= doesn't throw
}
//重载
shared_ptr& operator=(const shared_ptr& r) throw()
{
if(this== &r) return *this;
dispose(); //处理函数 释放，它里面封装着delete
px = r.px;
++*r.pn;
pn = r.pn;
return *this;
}
template<typename Y>
shared_ptr& operator=(const shared_ptr<Y>& r)//用于多态
{
dispose();
px = r.px;
++*r.pn;
pn = r.pn; //shared_count::op= doesn't throw
return *this;
}

~shared_ptr() { dispose(); }
void reset(T* p=0)
{
if ( px == p ) return;
if (--*pn == 0)
{ delete(px); }
else
{ // allocate newreference
// counter
// fix: prevent leak if new throws
try { pn = new size_type; }
catch (...) {
// undo effect of —*pn above to
// meet effects guarantee
++*pn;
delete(p);
throw;
} // catch
} // allocate newreference counter
*pn = 1;
px = p;
} // reset
reference operator*()const throw(){ return *px; }
pointer operator->()const throw(){ return px; }
pointer get() constthrow(){ returnpx; }
size_type use_count() constthrow()//
{ return *pn; }
bool unique() const throw()//
{ return *pn ==1; }
private:
void dispose() throw()
{
if (--*pn == 0)
{ delete px; delete pn; }
}
}; // shared_ptr
template<typename A,typenameB>
inline bool operator==(shared_ptr<A>const & l, shared_ptr<B> const & r)
{
return l.get() == r.get();
}
template<typename A,typenameB>
inline bool operator!=(shared_ptr<A>const & l, shared_ptr<B> const & r)
{
return l.get() != r.get();
}
}这是它的基本实现原理，接下来来一个它的实际例子，应用很简单！#include<boost/shared_ptr.hpp>
#include<iostream>
using namespace std;

class X
{
public:
X(){cout<< "gouzao"<<endl;}
~X()
{cout << "xigou"<<endl;}
};
int main(void)
{
boost::shared_ptr<X>p1(new X);
cout<<p1.use_count()<<endl;
boost::shared_ptr<X>p2 =p1;

cout<<p2.use_count()<<endl;
p1.reset();
cout<<p2.use_count()<<endl;
p2.reset();
system("pause");//这个可以忽略 因为我使用的是vs2010 防止它闪退 所以加了个终止命令！
return 0;

}