C++ vector和deque的区别

The difference between vector and deque

提问by rajenpandit

As vectorand dequeboth provides a function to push_backthe element at the last.

Asvector和dequebothpush_back最后为元素提供了一个函数。

where dequealso provides a function push_frontto insert the element at the beginning, which is bit costly in case of vector.

wheredeque还提供了push_front在开头插入元素的函数，在vector.

My question is when we can achieve the same functionality (push_back) of vectorby using deque, then why vectoris required?

我的问题是当我们可以通过使用实现相同的功能 ( push_back) 时，为什么需要？ vectordequevector

回答by paxdiablo

One main difference between vectors and deques is that the latter allows efficient insertion at the frontof the structure as well as the back.

向量和双端队列之间的一个主要区别是后者允许在结构的前面和后面有效插入。

Deques also do not guarantee that their elements are contiguous in memory so the at-style operator (indexing) may not be as efficient.

Deques 也不保证它们的元素在内存中是连续的，因此 at 风格的运算符（索引）可能效率不高。

Note that the difference is unlikely to matter in practice for smaller collections but would generally become more important if, for example, the collection size increases or you're modifying it manytimes per second.

请注意，对于较小的集合，这种差异在实践中不太可能重要，但如果例如集合大小增加或您每秒对其进行多次修改，则差异通常会变得更加重要。

回答by James Kanze

Performance, mainly. An std::dequehas all of the functionality of std::vector, at least for normal use, but indexing and iterating over it will typically be somewhat slower; the same may hold for appending at the end, if you've used reserve. And of course, std::vectoris the default container, using anything else will suggest to the reader that you have special requirements.

性能，主要是。Anstd::deque具有 的所有功能std::vector，至少对于正常使用而言，但对其进行索引和迭代通常会稍微慢一些；如果您使用了reserve. 当然，std::vector是默认容器，使用其他任何东西都会向读者暗示您有特殊要求。

std::vectoralso guarantees contiguity, so it (and only it) can be used to interface legacy functions which require a T*or a T const*.

std::vector还保证连续性，因此它（并且仅它）可用于接口需要 aT*或 a 的遗留函数T const*。

I might add that the one time I actually had a performance issue, and measured, std::vectorwas faster than std::deque, despitethe fact that I was regularly removing elements from the front (using the container as a queue, pushing at the back, and popping at the front). I don't know if that generalizes, however; in my case, the queue was relatively short (never more than about 15 elements, and usually many less), and the contents were char, which is extremely cheap to copy. But in general, I'd use std::vectoreven if I needed to remove elements from the front, if only because of its better locality. I'd probably only consider std::dequeif I expected thousands of elements, which were expensive to copy.

我可能会补充说，有一次我实际上遇到了性能问题并进行了测量，但std::vector比 快std::deque， 尽管我经常从前面删除元素（使用容器作为队列，在后面推，并在后面弹出）正面）。但是，我不知道这是否可以概括；就我而言，队列相对较短（从不超过大约 15 个元素，通常更少），内容为char，复制起来非常便宜。但总的来说，std::vector即使我需要从前面删除元素，我也会使用，因为它更好的局部性。我可能只会考虑std::deque是否需要数千个元素，而这些元素的复制成本很高。

回答by Marius Bancila

std::dequeis a double-ended queue. It provides efficient insertion and deletion of elements at the beginning also, not just at the end, as std::vectordoes. Vectors are guaranteed to store the elements in a contiguous storage, therefore you can access its elements by index/offset. std::dequedoes not offer this guarantee.

std::deque是一个双端队列。它也提供了有效的元素插入和删除，而不仅仅是在结尾，就像std::vector那样。向量保证将元素存储在连续存储中，因此您可以通过索引/偏移量访问其元素。std::deque不提供此保证。