问题描述
是否可以从头到尾迭代一个向量?
Is it possible to iterate a vector from the end to the beginning?
for (vector<my_class>::iterator i = my_vector.end();
i != my_vector.begin(); /* ?! */ ) {
}
或者只有这样的事情才有可能:
Or is that only possible with something like that:
for (int i = my_vector.size() - 1; i >= 0; --i) {
}
推荐答案
一种方法是:
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，增加一个 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，理论上，您的方法(使用 begin()/end() & --i)会起作用，std::vector 的迭代器是双向的，但请记住，end() 不是最后一个元素——它超出了最后一个元素，所以你必须递减首先，当你到达 begin() 时你就完成了——但你仍然需要进行处理.
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，我显然过于激进了.(重要的是 --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.)
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