C++智能指针的简单实现代码

#include <stdio.h>
#include <assert.h>
#include <string>

template <typename T>
class SmartPointer
{
public:
SmartPointer(T *p);
SmartPointer(const SmartPointer &pointer);
~SmartPointer();

SmartPointer<T>& operator=(SmartPointer<T> &pointer);
SmartPointer<T>& operator=(T *p);
T* operator->();
operator T*();

public:
size_t GetRefCounts() { return *ref_count_; }  // used for test

private:
void JustCopyData(const SmartPointer<T> &pointer);

private:
size_t *ref_count_;
T *p_;
};

template <typename T>
SmartPointer<T>::SmartPointer(T *p)
: ref_count_(new size_t(1)), p_(p)
{
}

template <typename T>
SmartPointer<T>::SmartPointer(const SmartPointer<T> &pointer)
{
JustCopyData(pointer);
++*ref_count_;
}

template <typename T>
SmartPointer<T>::~SmartPointer()
{
if (*ref_count_ == 1)
{
delete ref_count_;
delete p_;
}
else
{
--*ref_count_;
}
}

template <typename T>
SmartPointer<T>& SmartPointer<T>::operator=(SmartPointer<T> &pointer)
{
++*pointer.ref_count_;
this->~SmartPointer();
JustCopyData(pointer);
return *this;
}

template <typename T>
SmartPointer<T>& SmartPointer<T>::operator=(T *p)
{
this->~SmartPointer();
new (this) SmartPointer<T>(p);
return *this;
}

template <typename T>
SmartPointer<T>::operator T*()
{
return p_;
}

template <typename T>
T* SmartPointer<T>::operator->()
{
return p_;
}

template <typename T>
void SmartPointer<T>::JustCopyData(const SmartPointer<T> &pointer)
{
ref_count_ = pointer.ref_count_;
p_ = pointer.p_;
}

void TestSmartPointer()
{
typedef std::string TestType;
TestType *p = new TestType("abc");
SmartPointer<TestType> pointer(p);
assert(pointer.GetRefCounts() == 1);

{
SmartPointer<TestType> local_pointer = pointer;
assert(p == local_pointer);
assert(local_pointer.GetRefCounts() == 2);
assert(local_pointer->size() == p->size());

pointer = new TestType();
assert(local_pointer.GetRefCounts() == 1);

SmartPointer<TestType> local_pointer2(pointer);
local_pointer2 = local_pointer;
assert(local_pointer.GetRefCounts() == 2);
assert(p == local_pointer2);
}
assert(p != pointer);
assert(pointer.GetRefCounts() == 1);
}

int main()
{
TestSmartPointer();
return 0;
}