巧用std::shared_ptr全局對象釋放單例內存

巧用std::shared_ptr

單例的使用相對比較廣泛，但是需要在程序退出前調用它的析構函數對數據進行釋放，常規做法是在main函數末尾進行釋放工作，

但是這樣相對比較繁瑣，因此便有了利用全局變量由系統負載析構的特點，定義一個全局str::shared_ptr對象，對象指定對單例進行析構。

因此不需要我們關心何時析構單例，堪稱方便。

　　SingleObject.hpp

#ifndef SINGLEOBJECT_H
#define SINGLEOBJECT_H

class SingleObject
{
public:
	static SingleObject& GetInstance();
	static SingleObject* GetInstancePtr();
	static void DoSomeThing();
	static void DelObj();
private:
	static void NewObj();
	SingleObject();
	~SingleObject();
	
	static SingleObject* msObj;
};

#endif // SINGLEOBJECT_H

　　SingleObject.cpp

#include "SingleObject.hpp"
#include <iostream>
#include <memory>

std::shared_ptr<SingleObject> SingleObjectDeletor( SingleObject::GetInstancePtr(), [](SingleObject *){ SingleObject::GetInstance().DelObj(); });

SingleObject* SingleObject::msObj = NULL;

SingleObject::SingleObject()
{
	std::cout << "This is the constructor of SignleObject class!\n";
}

SingleObject::~SingleObject()
{
	std::cout << "This is the destructor of SingleObject class!\n";
}

void SingleObject::NewObj()
{
	if( NULL == msObj )
	{
		// lock
		msObj = new SingleObject();
		
		// unlock
	}
	
	std::cout << "New an object, address: " << +msObj << std::endl;
}

void SingleObject::DelObj()
{
	if( NULL != msObj )
	{
		delete msObj;
		std::cout << "Delete an object!\n";
	}
}

SingleObject* SingleObject::GetInstancePtr()
{
	if( NULL == msObj )
	{
		NewObj();
	}
	
	return msObj;
}

SingleObject& SingleObject::GetInstance()
{
	if( NULL == msObj )
	{
		NewObj();
	}
	
	return *msObj;
}

void SingleObject::DoSomeThing()
{
	std::cout << "SingleObject do some thing!\n";
}

　　main.cpp

#include <iostream>
#include "SingleObject.hpp"

int main(int argc, char **argv)
{
	SingleObject::GetInstance().DoSomeThing();
	
	return 0;
}

　　輸出：