关于 C++ stl容器交换函数

发布于 2024-08-27 11:59:31 字数 184 浏览 9 评论 0原文

最近了解到所有的stl容器都有swap功能： ie

c1.swap(c2);

将导致底层对象 c1 被分配给 c2，反之亦然。我问我的教授，如果 c1 和 c2 是参考文献，是否也是如此。他说遵循同样的机制。

我想知道这是怎么发生的，因为 C++ 引用无法重置。

原文

I recently learned that all stl containers have swap function:
i.e.

c1.swap(c2);

will lead to object underlying c1 being assigned to c2 and vice versa.
I asked my professor if same is true in case of c1 and c2 being references.
he said same mechanism is followed.

I wonder how it happens since c++ references cannot be reseted.

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奢欲 2024-09-03 11:59:31

引用是别名。如果您有两个引用，调用 swap 将交换它们所引用的内容，而不是引用本身。

C& r1 = c1; // r1 references c1
C& r2 = c2; // r2 references c2

r1.swap(r2); // same as c1.swap(c2)

交换的不是变量，而是使它们在逻辑上独立的因素。如果一个容器仅包含一个指针，如果您将该指针与另一个容器的指针交换，那么您就有效交换了容器。变量本身仍然存在。

具体例子：

typedef std::vector<int> vec;

vec c1;
vec c2;

// fill em up

c1.swap(c2);
/*
A vector, internally, has a pointer to a chunk of memory (and some other stuff).
swap() is going to swap the internal pointer (and other stuff) with the other
container. They are logically swapped.
*/

vec& r1 = c1; // r1 is an alias for c1
vec& r2 = c2; // r2 is an alias for c2

r1.swap(r2); // same as c1.swap(c2). they are now unswapped

References are aliases. If you have two references, calling swap will swap what they are referring to, not the references themselves.

C& r1 = c1; // r1 references c1
C& r2 = c2; // r2 references c2

r1.swap(r2); // same as c1.swap(c2)

And it's not the variables that get swapped, it's what make them logically independent that gets swapped. If a container only consists of a pointer, if you swap that pointer with the pointer of another container, you've effectively swapped the containers. The variables themselves remain.

Concrete example:

typedef std::vector<int> vec;

vec c1;
vec c2;

// fill em up

c1.swap(c2);
/*
A vector, internally, has a pointer to a chunk of memory (and some other stuff).
swap() is going to swap the internal pointer (and other stuff) with the other
container. They are logically swapped.
*/

vec& r1 = c1; // r1 is an alias for c1
vec& r2 = c2; // r2 is an alias for c2

r1.swap(r2); // same as c1.swap(c2). they are now unswapped

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や三分注定 2024-09-03 11:59:31

正在交换的是容器的内容，即 c1 的元素被移动到 c2，反之亦然。玩具实现可能如下所示：

template <class T>
class vector {
    void swap(vector& other) {
        swap(other.m_elements, m_elements);
        swap(other.m_size, m_size):
    }
    T* m_elements;
    size_t m_size;
};

It's the content of the containers that's being swapped, i.e. the elements of c1 are moved to c2 and vice versa. A toy implementation could look something like this:

template <class T>
class vector {
    void swap(vector& other) {
        swap(other.m_elements, m_elements);
        swap(other.m_size, m_size):
    }
    T* m_elements;
    size_t m_size;
};

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