获取std :: vector的迭代器索引的最有效方法是什么？ [英] What is the most effective way to get the index of an iterator of an std::vector?

问题描述

我正在遍历一个向量，需要迭代器当前指向的索引。 AFAIK这可以通过两种方式完成：

I'm iterating over a vector and need the index the iterator is currently pointing at. AFAIK this can be done in two ways:

• it - vec.begin（）


• std :: distance（vec.begin（），it）

• it - vec.begin()
• std::distance(vec.begin(), it)

这些方法的优点和缺点是什么？

What are the pros and cons of these methods?

推荐答案

我更喜欢 it - vec.begin（）正是由于Naveen给出的相反原因：如果将向量更改为列表，将不会编译。如果你在每次迭代中都这样做，你很容易就会把O（n）算法变成O（n ^ 2）算法。

I would prefer it - vec.begin() precisely for the opposite reason given by Naveen: so it wouldn't compile if you change the vector into a list. If you do this during every iteration, you could easily end up turning an O(n) algorithm into an O(n^2) algorithm.

另一种选择，如果你迭代期间不要在容器中跳转，将索引保持为第二个循环计数器。

Another option, if you don't jump around in the container during iteration, would be to keep the index as a second loop counter.

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