从集合中的任意索引获取元素 [英] Get element from arbitrary index in set

问题描述

我有一组类型为 set< int> 的类型，我想让一个迭代器到达一个不是开始的地方.

I have a set of type set<int> and I want to get an iterator to someplace that is not the beginning.

我正在执行以下操作:

set<int>::iterator it = myset.begin() + 5;

我很好奇为什么这样做不起作用，以及将迭代器添加到我想要的位置的正确方法是什么.

I am curious why this is not working and what is the correct way to get an iterator to where I want it.

推荐答案

myset.begin()+ 5; 仅适用于随机访问迭代器，该迭代器来自 std :: set不是.

myset.begin() + 5; only works for random access iterators, which the iterators from std::set are not.

对于输入迭代器，有功能 std :: advance :

For input iterators, there's the function std::advance:

set<int>::iterator it = myset.begin();
std::advance(it, 5); // now it is advanced by five

在C ++ 11中，还有 std :: next ，这很相似，但不会更改其参数:

In C++11, there's also std::next which is similar but doesn't change its argument:

auto it = std::next(myset.begin(), 5);

std :: next 需要一个正向迭代器.但是由于 std :: set< int> :: iterator 是双向迭代器，因此 advance 和 next 都可以使用.

std::next requires a forward iterator. But since std::set<int>::iterator is a bidirectional iterator, both advance and next will work.

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