从头到尾迭代C ++向量 [英] Iterating C++ vector from the end to the beginning

问题描述

是否可以从头到尾迭代矢量？

Is it possible to iterate a vector from the end to the begin?

for (vector<my_class>::iterator i = my_vector.end();
        i != my_vector.begin(); /* ?! */ ) {
}

或者这仅可能通过以下方式实现：

Or is that only possible with something like that:

for (int i = my_vector.size() - 1; i >= 0; --i) {
}

推荐答案

最好的方法是：

for (vector<my_class>::reverse_iterator i = my_vector.rbegin(); 
        i != my_vector.rend(); ++i ) { 
} 

rbegin（） / rend（）是专门为此目的而设计的。 （是的，增加 reverse_interator 会将其向后移动。）

rbegin()/rend() were especially designed for that purpose. (And yes, incrementing a reverse_interator moves it backward.)

现在，从理论上讲，您的方法（使用 begin（） / end（）& -i ）可以工作， std :: vector 的迭代器是双向的，但是请记住， end（）不是最后一个元素—它超出了最后一个元素，因此您必须先递减，然后在达到 begin（）—时完成。

Now, in theory, your method (using begin()/end() & --i) would work, std::vector's iterator being bidirectional, but remember, end() isn't the last element — it's one beyond the last element, so you'd have to decrement first, and you are done when you reach begin() — but you still have to do your processing.

vector<my_class>::iterator i = my_vector.end();
while (i != my_vector.begin())
{
     --i;
    /*do stuff */

} 

更新：在将 for（）循环重写为 while（）循环时，我显然过于激进。 （重要的部分是-i 在开头。）

UPDATE: I was apparently too aggressive in re-writing the for() loop into a while() loop. (The important part is that the --i is at the beginning.)

这篇关于从头到尾迭代C ++向量的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！