使用 shared_ptr

标签：shared_ptr   boost   

shared_ptr是一個模板類，它保存了一個指向動態分配的對象的指針，當指向這個對象的最後一個shared_ptr被銷燬的時候，這個對象也被銷燬了。

有三種使用 shared_ptr的方法：

1)使用 std::shared_ptr

要用 std::shared_ptr的方式使用。

實例代碼：

#include <iostream>
#include <memory>
class A
{
public:
	A() 
	{
		std::cout <<"A constructor" << std::endl;
		a = new int(3);	
	}
	~A() 
	{
		std::cout <<"A destructor" << std::endl;
		delete a;
		a = NULL;
	}
	void Print(void)
	{
		std::cout << "a = " <<*a << std::endl;
	}
private:
	int *a;
};

void foo(std::shared_ptr<A> pA)
{
	std::cout <<"user count : ##" << pA.use_count() << std::endl;
	std::shared_ptr <A> pB = pA;
	std::cout <<"user count : ###" << pA.use_count() << std::endl;
	pB.get()->Print();
}

int main(void)
{
	std::shared_ptr<A> p1 (new A);
	std::cout << "use count #" << p1.use_count() << std::endl;
	foo(p1);
	std::cout << "use count ####" << p1.use_count() << std::endl;
	return 0;
}

2）使用  tr1:shared_ptr

要用std:tr1::shared_ptr的方式使用

實例代碼：

#include <iostream>
#include <tr1/memory>

class A
{
public:
	A() 
	{
		std::cout <<"A constructor" << std::endl;
		a = new int(3);	
	}
	~A() 
	{
		std::cout <<"A destructor" << std::endl;
		delete a;
		a = NULL;
	}
	void Print(void)
	{
		std::cout << "a = " <<*a << std::endl;
	}
private:
	int *a;
};

void foo(std::tr1::shared_ptr<A> pA)
{
	std::cout <<"user count : ##" << pA.use_count() << std::endl;
	std::tr1::shared_ptr <A> pB = pA;
	std::cout <<"user count : ###" << pA.use_count() << std::endl;
	pB.get()->Print();
}

int main(void)
{
	std::tr1::shared_ptr<A> p1 (new A);
	std::cout << "use count #" << p1.use_count() << std::endl;
	foo(p1);
	std::cout << "use count ####" << p1.use_count() << std::endl;
	return 0;
}

3）使用 boost庫。

要先確保已經安裝了 boost庫。在 ubuntu上，可以用下面的方法檢查：

$ dpkg --get-selections  | grep boost
libboost-date-time1.54.0:i386			install
libboost-dev					install
libboost-iostreams1.54.0:i386			install
libboost-system1.54.0:i386			install
libboost1.54-dev				install

要用 boost::shared_ptr的方式使用。
實例代碼:

#include <iostream>
//#include <memory>
#include <boost/tr1/tr1/memory>

class A
{
public:
	A() 
	{
		std::cout <<"A constructor" << std::endl;
		a = new int(3);	
	}
	~A() 
	{
		std::cout <<"A destructor" << std::endl;
		delete a;
		a = NULL;
	}
	void Print(void)
	{
		std::cout << "a = " <<*a << std::endl;
	}
private:
	int *a;
};

void foo(boost::shared_ptr<A> pA)
{
	std::cout <<"user count : ##" << pA.use_count() << std::endl;
	boost::shared_ptr <A> pB = pA;
	std::cout <<"user count : ###" << pA.use_count() << std::endl;
	pB.get()->Print();
}

int main(void)
{
	boost::shared_ptr<A> p1 (new A);
	std::cout << "use count #" << p1.use_count() << std::endl;
	foo(p1);
	std::cout << "use count ####" << p1.use_count() << std::endl;
	return 0;
}

References:

1) http://stackoverflow.com/questions/2918202/where-is-shared-ptr

2)http://www.boost.org/doc/libs/1_58_0/libs/smart_ptr/shared_ptr.htm

使用 shared_ptr

标签：shared_ptr   boost   

原文地址：http://blog.csdn.net/caspiansea/article/details/46275413