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| #include <bits/stdc++.h>
#include <type_traits>
using namespace std;
class Point
{
public:
int a;
int b;
int c;
public:
Point() = default;
Point(int _a, int _b, int _c) : a(_a), b(_b), c(_c) {}
};
template <typename _Tp>
class _Ref_count
{
private:
_Tp *_M_ptr;
int _M_use_count;
int _M_weak_count;
public:
_Ref_count(_Tp *_Px)
{
_M_ptr = _Px;
_M_use_count = 1;
_M_weak_count = 1;
}
void _Decref()
{
_M_use_count--;
_M_weak_count--;
if (_M_weak_count == 0)
{
delete _M_ptr;
delete this;
}
}
void _Incref()
{
_M_use_count++;
_M_weak_count++;
}
int _Get_uses() const
{
return _M_use_count;
}
};
template <typename _Tp>
class shared_pointer
{
private:
_Ref_count<_Tp> *_M_refcount;
_Tp *_M_ptr;
public:
shared_pointer(_Tp *_Px)
{
_M_ptr = _Px;
_M_refcount = new _Ref_count(_Px);
}
shared_pointer(shared_pointer<_Tp> &_Sp)
{
_M_refcount = _Sp._M_refcount;
_M_ptr = _Sp._M_ptr;
_M_refcount->_Incref();
}
~shared_pointer()
{
_M_refcount->_Decref();
}
_Tp *get()
{
return _M_ptr;
}
int use_count()
{
return _M_refcount->_Get_uses();
}
void reset(_Tp *_Px)
{
shared_pointer<_Tp>(_Px).swap(*this);
}
void reset()
{
_M_refcount->_Decref();
_M_refcount = nullptr;
_M_ptr = nullptr;
}
void swap(shared_pointer &_Right)
{
std::swap(_M_ptr, _Right._M_ptr);
std::swap(_M_refcount, _Right._M_refcount);
}
explicit operator bool() const
{
return use_count() != 0;
}
_Tp operator*() const noexcept
{
return *_M_ptr;
}
_Tp *operator->() const noexcept
{
return _M_ptr;
}
};
int main()
{
shared_pointer<Point> sp1(new Point(1, 2, 3));
cout << "访问元素：\n";
cout << sp1->a << sp1->b << "\n";
cout << "获取引用计数：\n";
cout << sp1.use_count() << "\n";
shared_pointer<Point> sp2 = sp1;
auto sp3(sp1);
cout << "构造sp2和sp3后的引用计数：\n";
cout << sp1.use_count() << "\n";
cout << sp2.use_count() << "\n";
cout << sp3.use_count() << "\n";
cout << "reset sp3后：\n";
sp3.reset(new Point(3, 2, 1));
cout << sp1.use_count() << "\n";
cout << sp2.use_count() << "\n";
cout << sp3.use_count() << "\n";
cout << sp3->a << sp3->b << "\n";
return 0;
}
|
