C++中基于范围的for循环是否会保留索引顺序 [英] Will range based for loop in c++ preserve the index order

问题描述

在 c++11 中，如果我在向量上使用基于范围的 for 循环，它会保证迭代顺序吗?

In c++11, if I use a range based for loop on vector, will it guarantee the iteration order?

即以下代码块是否保证产生相同的输出?

i.e. are the following code blocks guaranteed to produce the same output?

vector<T> output;
vector<U> V;
for( auto v: V) output.push_back(f(v));

对比

for(int i =0; i < V.size(); ++i) output.push_back(f(V[i])); 

如果不是vector而是map等怎么办?

what if it is not vector but map, etc?

推荐答案

是的，这两个代码保证做同样的事情.虽然我没有标准的链接，你可以看看这里.我引用:您可以将其读作对于 v 中的所有 x"，从 v.begin() 开始并迭代到 v.end().

Yes the two codes are guaranteed to do the same. Though I don't have a link to the standard you can have a look here. I quote: You can read that as "for all x in v" going through starting with v.begin() and iterating to v.end().

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