向量推回对元素地址的影响 [英] Effects of vector pushback on element address

问题描述

我有一个类对象的向量.一个函数随机选择两个元素并返回它们的地址.

I have a vector of class objects. A function randomly choses two elements and return their addresses.

现在使用这两个元素，我想生成两个相同类的新对象，并通过使用push_back将它们添加到向量中.

Now using these two elements, I want to generate two new objects of the same class and add them to the vector by using push_back.

这是两个父元素的地址:

Here is the address of the two parent elements:

这里没问题.然后生成第一个子对象，我使用vector_pushback将其添加到向量的末尾.问题是，在执行push_back命令之后，父对象的地址似乎已更改.这是push_back之后的调试器状态:

No problem here. The first child object is then generated, and I use vector_pushback to add it to the end of the vector. The problem is, after the push_back command has been executed, it seems like the addresses of the parent objects change. Here is the state of debugger after push_back:

如您所见，地址显然保持不变，但似乎它们指向push_back之后的垃圾值.据我了解，push_back在向量的末尾添加了一个元素.因此，我希望这两个元素的地址完全不变.

As you can see, the addresses obviously stay the same, but it seems like they point to garbage values after push_back. To my understanding, push_back adds an element at the end of the vector. Therefore I expect the address of the 2 elements to not change at all.

怎么了?

推荐答案

TL; DR版本:

插入操作可以使<元素的任何指针，引用或迭代器无效code> std :: vector .

完整说明:

std :: vector 具有两个有用的指标:

A std::vector has two useful metrics:

• size ，即存储的元素数量.
• capacity ，当前可以存储的元素数量.

容量> =大小始终.

capability 是内部动态分配的数组的长度. ^* 插入元素时， size 递增1.但是一旦达到 capacity ，就必须分配一个更大的新数组(因此会增加 capacity ).这要求复制所有元素，并删除原始元素.所以他们所有的地址都改变了.

The capacity is the length of the internal dynamically-allocated array.^* When you insert an element, the size increments by 1. But once it reaches capacity, a new, larger array must be allocated (hence increasing the capacity). This requires all the elements to be copied across, and the originals to be deleted. So all their addresses change.

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_{*这是 std :: vector 的典型内部实现.}

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_{* This is the typical internal implementation of a std::vector.}

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