[英]Transferring std::unique_ptr between Widgets
I have a Widget class, which is supposed to have unique ownership of another Widget. 我有一个Widget类,应该具有另一个Widget的唯一所有权。 I want to implement a function which passes this Widget to another Widget. 我想实现一个将此小部件传递给另一个小部件的功能。 I learnt that the best way to implement the concept of single ownership is std::unique_ptr
, however I can't get it to run 我了解到,实现单一所有权概念的最佳方法是std::unique_ptr
,但是我无法使其运行
This is the code: 这是代码:
class Widget
{
public:
Widget(void) { }
virtual ~Widget(void) { /* */ }
void successor(Widget&& successor)
{
this->_successor = std::unique_ptr<Widget>(&successor);
}
void refer_value(int a)
{
_successor->value = a;
}
auto refer_value(void) const -> int
{
return _successor->value;
}
auto get(void) -> Widget&
{
return *_successor;
}
int value;
private:
std::unique_ptr<Widget> _successor;
};
It compiles without a problem, but when I try to run this: 编译没有问题,但是当我尝试运行此命令时:
int main(void)
{
Widget a{};
Widget b{};
Widget c{};
a.successor(Widget{});
a.refer_value(5);
b.successor(std::move(a.get()));
std::cout << b.refer_value();
}
I get a Segmentation Fault. 我遇到了细分错误。 What is the problem? 问题是什么?
And additionally, How would I have to write an implementation of the successor() function, if I wanted to pass Widget c
. 另外,如果我想传递Widget c
,我将不得不如何编写一个successor()函数的实现。 I could only get it running for rvalues. 我只能让它为右值运行。
Here 这里
this->_successor = std::unique_ptr<Widget>(&successor);
You're creating a unique_ptr
to an object that would be destroyed once the scope exits. 您正在为对象创建一个unique_ptr
,一旦范围退出,该对象将被销毁。
Also, here 也在这里
b.successor(std::move(a.get()));
You're taking the address of an existing pointer in a unique_ptr
, and assigning it to yet another unique_ptr
. 您要在unique_ptr
现有指针的地址,并将其分配给另一个 unique_ptr
。 It's basically wrong/double deallocations all over the place here. 在这里到处都是错误/双重释放。
I'm highly unaware of what you're trying to do here. 我不知道高度的你想在这里做什么。 At any rate, if I can just limit myself to the number of changes relevant to memory management here in order to have this code make sense: 无论如何,如果我可以将自己限制在与内存管理相关的更改数量上,以使此代码有意义:
class Widget
{
public:
Widget(void) { }
virtual ~Widget(void) { /* */ }
void successor(std::shared_ptr<Widget> successor)
{
this->_successor = std::move(successor);
}
void refer_value(int a)
{
_successor->value = a;
}
auto refer_value(void) const -> int
{
return _successor->value;
}
std::shared_ptr<Widget> get()
{
return _successor;
}
int value;
private:
std::shared_ptr<Widget> _successor;
};
int main(void)
{
Widget a{};
Widget b{};
Widget c{};
a.successor(std::make_shared<Widget>());
a.refer_value(5);
b.successor(a.get());
std::cout << b.refer_value();
}
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