std :: shared_ptr这个 [英] std::shared_ptr of this
问题描述
我目前正在尝试学习如何使用智能指针。但是,在做一些实验时,我发现了以下情况,我找不到一个饱和的解决方案:
想象你有一个对象的类A是类的对象的父类B(孩子),但两者应该彼此认识:
A类;
class B;
class A
{
public:
void addChild(std :: shared_ptr< B> child)
{
children-> push_back(child);
//如何正确传递指针?
// child-> setParent(this); // wrong
// ^^^^
}
private:
std :: list< std :: shared_ptr< B>儿童;
};
class B
{
public:
setParent(std :: shared_ptr< A> parent)
{
this-> parent = parent;
};
private:
std :: shared_ptr< A>父母
};问题是A类的对象如何传递一个 std ::
有Boost的解决方案( this
共享指针(获取 boost :: shared_ptr
this
),但是如何使用 std ::
智能指针处理这个问题? / p>
解决方案有 std :: enable_shared_from_this
仅用于此目的。您可以继承它,并且可以调用 .shared_from_this()
。此外,您在此处创建循环依赖性,这可能导致资源泄漏。这可以使用 std :: weak_ptr
。所以你的代码可能看起来像这样(假设孩子依赖父的存在,而不是相反):
class A;
class B;
class A
:public std :: enable_shared_from_this< A>
{
public:
void addChild(std :: shared_ptr< B> child)
{
children.push_back(child);
//像这样
child-> setParent(shared_from_this()); // ok
// ^^^^^^^^^^^^^^^^^
}
private:
// note weak_ptr
std :: list< std :: weak_ptr< B>>儿童;
// ^^^^^^^^
};
class B
{
public:
void setParent(std :: shared_ptr< A> parent)
{
this-> parent = parent;
}
private:
std :: shared_ptr< A>父母
};
但是,调用 .shared_from_this()
要求此
在呼叫时由 std :: shared_ptr
拥有。这意味着你不能在堆栈上创建这样的对象,并且不能在构造函数或析构函数中调用 .shared_from_this()
。
I am currently trying to learn how to use smart pointers. However while doing some experiments I discovered the following situation for which I could not find a satifying solution:
Imagine you have an object of class A being parent of an object of class B (the child), but both should know each other:
class A;
class B;
class A
{
public:
void addChild(std::shared_ptr<B> child)
{
children->push_back(child);
// How to do pass the pointer correctly?
// child->setParent(this); // wrong
// ^^^^
}
private:
std::list<std::shared_ptr<B>> children;
};
class B
{
public:
setParent(std::shared_ptr<A> parent)
{
this->parent = parent;
};
private:
std::shared_ptr<A> parent;
};
The question is how can an object of class A pass a std::shared_ptr
of itself (this
) to its child?
There are solutions for Boost shared pointers (Getting a boost::shared_ptr
for this
), but how to handle this using the std::
smart pointers?
解决方案 There is std::enable_shared_from_this
just for this purpose. You inherit from it and you can call .shared_from_this()
from inside the class. Also you are creating circular dependencies here that can lead to resource leaks. That can be resolved with the use of std::weak_ptr
. So your code might look like this (assuming children rely on existence of parent and not the other way around):
class A;
class B;
class A
: public std::enable_shared_from_this<A>
{
public:
void addChild(std::shared_ptr<B> child)
{
children.push_back(child);
// like this
child->setParent(shared_from_this()); // ok
// ^^^^^^^^^^^^^^^^^^
}
private:
// note weak_ptr
std::list<std::weak_ptr<B>> children;
// ^^^^^^^^
};
class B
{
public:
void setParent(std::shared_ptr<A> parent)
{
this->parent = parent;
}
private:
std::shared_ptr<A> parent;
};
Note however, that calling .shared_from_this()
requires that this
is owned by std::shared_ptr
at the point of call. This means that you cannot create such object on stack anymore, and cannot call .shared_from_this()
from within a constructor or destructor.
这篇关于std :: shared_ptr这个的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!