迭代时删除

发布于 2024-09-27 00:42:10 字数 894 浏览 1 评论 0原文

可能的重复：
Vector.erase(Iterator) 导致内存访问错误
 迭代向量，删除某些项目。

嗨，我写了这个，但运行时遇到一些错误

for (vector< vector<Point> >::iterator track = tracks_.begin(); track != tracks_.end(); track++) {
        if (track->empty()) { // if track is empty, remove it
            tracks_.erase(track);
            track++; // is this ok?
        }else {   //if there are points, deque
            track->erase(track->begin()); //my program crashes here after a while... ;(
        }
    }

我有一个由点向量组成的向量（2个整数），我将其称为轨道（1个轨道是1个点向量）我想检查每个轨道，如果它们包含点，则删除第一个轨道，否则删除轨道。这是正确的吗？

提前致谢。

原文

Possible Duplicates:
Vector.erase(Iterator) causes bad memory access
iterate vector, remove certain items as I go.

Hi,
I wrote this but I am get some errors when running it

for (vector< vector<Point> >::iterator track = tracks_.begin(); track != tracks_.end(); track++) {
        if (track->empty()) { // if track is empty, remove it
            tracks_.erase(track);
            track++; // is this ok?
        }else {   //if there are points, deque
            track->erase(track->begin()); //my program crashes here after a while... ;(
        }
    }

I have a vector of vector of points (2 ints) whose I call tracks (1 track is 1 vector of points)
I want to check each track and if they contain points then delete the first one otherwise delete the track. Is this correct?

Thanks in advance.

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旧时光的容颜 2024-10-04 00:42:10

向量的 erase() 使现有迭代器无效，但它返回一个新的迭代器，指向被删除的元素之后的元素。返回的迭代器可用于继续迭代向量。

你的循环可以这样写：

vector< vector<Point> >::iterator track = tracks_.begin();
while (track != tracks_.end()) {
    if (track->empty()) {
        // if track is empty, remove it
        track = tracks_.erase(track);
    }
    else {
        //if there are points, deque
        track->erase(track->begin());
        ++track;
    }
}

A vector's erase() invalidates existing iterators, but it returns a new iterator pointing to the element after the one that was removed. This returned iterator can be used to continue iterating over the vector.

Your loop could be written like this:

vector< vector<Point> >::iterator track = tracks_.begin();
while (track != tracks_.end()) {
    if (track->empty()) {
        // if track is empty, remove it
        track = tracks_.erase(track);
    }
    else {
        //if there are points, deque
        track->erase(track->begin());
        ++track;
    }
}

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