共享指针的问题 [英] problems with shared pointers

问题描述

您好，我是论坛新手，这是我的第一个问题，但最近我遇到了一些奇怪的行为.

我有两个班Goo和Foo.我在Foo中有一个方法，该方法返回Goo类型的共享指针.一切都可以编译...但是当我调试它时，我看到创建了2个类型为Goo的对象，并且Foo中的成员类从未得到值.

这是代码:

Hello I''n new on the forum, meaning It''s my first question asked but I recently came across some strange behavior.

I have two classes Goo and Foo. I have a method in Foo that returns a shared pointer of type Goo. It all compiles ok...but when I debug it I can see that 2 objects are created of type Goo and the member class inside Foo never gets a value.

here''s the code :

#include <memory>
#include <iostream>
#include <vector>
using namespace std;

class Goo
{
	int y;
public:
	Goo(){}
	~Goo(){}
	void set_y(int new_val) 
	{
		y=new_val;
	}

};

class Foo
{
	
	int x;
	//shared_ptr<Goo> gooptr;
	Goo Goomem;

	public:

	Foo(int val=0) :x(val) {}
	~Foo(){cout<<"desctructed";}
	
	void do_something() 
	{
		cout<<"doing nothing..."<<endl;
	}
	void set_x(int new_val) 
	{
		x=new_val;
	}
	void show_x() const {cout<< x<<endl; }
	shared_ptr<Goo> getshared()
	{
		shared_ptr<Goo> gooptr = make_shared<Goo>(Goomem);
		return gooptr;
	}

};


int main()
{
	bool expired=false;
	shared_ptr<Foo> pf (new Foo); 

	shared_ptr<Goo>gp=(*pf).getshared();
	(*gp).set_y(1);
	gp=(*pf).getshared();
	(*gp).set_y(2);
	gp=(*pf).getshared();
	(*gp).set_y(3);
	gp=(*pf).getshared();
	(*gp).set_y(4);
	gp=(*pf).getshared();

	pf.reset();

	return 0;
}

我肯定缺少某些东西...我的意思是我认为make_shared实际上每次都会创建一个新实例，并且由于没有其他指向该实例的智能指针，因为我重新分配了goo指针，所以它得到了收集的垃圾?我不知道...(很抱歉，这对您来说很明显，但是我才刚开始了解它们和C语言).

There must be something I''m missing...I mean I think that make_shared actually creates a new instance every time and since there are no more smart pointers that point to it, since i''m reassigning the goo pointer, it get''s garbage collected ? I don''t know...(Sorry if it''s obvious for you but I just started to learn about them and C in general)

推荐答案

方法:

shared_ptr<goo> getshared()
{
	shared_ptr<goo> gooptr = make_shared<goo>(Goomem);
        return gooptr;
}</goo></goo></goo>

每次调用Goo都会重新创建它的一个新实例，并且旧实例会被垃圾回收，因为不再引用它了.
这就是我实际上在Goo中写值的方式

reates a new instance of Goo each time it is called and the old instance get''s garbage colected because the are no more references to it.
this is how I actually wrote the value inside Goo

(*pf).setgoo((*gp).get_y());

如果你问我的话很漂亮的意大利面条. 感谢所有人

pretty spaghetti if you ask me...but it worked
thanks to all

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