迭代C ++向量从结尾到开始 [英] Iterating C++ vector from the end to the begin
问题描述
是否有可能从末端到开始迭代一个向量?
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(); /* ?! */ ) {
}
或者只有这样:
for (int i = my_vector.size() - 1; i >= 0; --i) {
}
推荐答案
好,最好的方法是:
for (vector<my_class>::reverse_iterator i = my_vector.rbegin();
i != my_vector.rend(); ++i ) {
}
rbegin()/ rend()专门为此目的而设计。 (和是的,增加一个reverse_interator向后移动)
rbegin()/rend() especically designed for that purpose. (And yes, incrementing a reverse_interator moves it backward)
现在,理论上你的方法(使用begin / end& / code>)将工作,vector的迭代器是双向的,但是请记住,end()不是最后一个元素 - 它是一个超出最后一个元素,所以你必须递减,你到达begin() - 但你还是要做你的处理。
Now, in theory, your method (using begin/end & --i
) would work, 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 */ )
}
:我显然是太积极重写for()循环到一个while循环。 (重要部分是 - i
在开头。)
UPDATE: I was apparently too aggressive in re-writing the for() loop into a while loop. (The important part is the the --i
is at the beginning.)
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