C++インテリジェントポインタの簡単な実装コード

2503 ワード

一部のテストコードが付属しています
#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;
}