获取 std::vector 的迭代器索引的最有效方法是什么?

沃梦达教程 C/C++问题

2022-01-01

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

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问题描述

我正在迭代一个向量并且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:

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

这些方法的优缺点是什么?

What are the pros and cons of these methods?

推荐答案

我更喜欢 it - vec.begin() 正是因为 Naveen 给出的相反原因:所以它 wouldn'如果将向量更改为列表，则可以编译.如果你在每次迭代中都这样做，你很容易最终将 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.

如果您在迭代期间不在容器中跳转，另一种选择是将索引保留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.

注意:it是容器迭代器的通用名称，std::container_type::iterator it;.

Note: it is a common name for a container iterator,std::container_type::iterator it;.

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