std :: shared_ptr：reset（）与分配 [英] std::shared_ptr: reset() vs. assignment
问题描述
这是一个基本问题，但是我没有找到有关它的先前文章。以下问题的标题听起来可能与我的问题相同，但问题本身与标题不匹配：
This is a basic question, but I did not find a previous post about it. The title of the following question sounds like it might be the same question as mine, but the question itself does not match the title: is it better to use shared_ptr.reset or operator =?
我很困惑 std :: shared_ptr 的 reset（）成员函数的目的：除了赋值外，它还有什么作用
I am confused about the purpose of the reset() member function of std::shared_ptr: what does it contribute in addition to the assignment operator?
具体来说，给定定义：
auto p = std::make_shared<int>(1);
-
以下两行等效：
Are the following two lines equivalent:
p = std::make_shared<int>(5);
p.reset(new int(5));
这些怎么办：
What about these:
p = nullptr;
p.reset();
如果在两种情况下这两行都相等，那么 reset（）的目的是什么？
If the two lines are equivalent in both cases, then what is the purpose of reset()?
编辑：让我重新表述这个问题，以更好地强调它的观点。问题是：是否存在 reset（）让我们实现没有它就不容易实现的事情？
Let me re-phrase the question to better emphasize its point. The question is: is there a case where reset() lets us achieve something that is not as easily achievable without it?
推荐答案
使用 reset（）时，传递给reset的参数不必是托管对象（也不能是）。而对于 = 而言，右侧必须是一个托管对象。
When using reset() the parameter passed to reset need not be a managed object (nor can it be); whereas with = the right hand side must be a managed object.
因此，这两行为您提供相同的目的结果：
So these two lines give you the same end result:
p = std::make_shared<int>(5); // assign to a newly created shared pointer
p.reset(new int(5)); // take control of a newly created pointer
但是我们不能这样做：
p = new int(5); // compiler error no suitable overload
p.reset(std::make_shared<int>(5).get()); // uh oh undefined behavior
没有 reset（）如果不创建共享指针并对其进行分配，就无法将共享指针重新分配给其他原始指针。没有 = ，您将无法使共享指针指向另一个共享指针。
Without reset() you would not be able to reassign a shared pointer to a different raw pointer without creating a shared pointer and assigning it. Without = you wouldn't be able to make a shared pointer point to another shared pointer.
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