c++ - 迭代器与非迭代器循环，不同的输出，C++

Question

我的项目中有以下代码:

std::cout << "Without iterator:\n";

std::vector<RectangleCluster*> rc = p->getInnerRegionPolygons().at(0)->getClusters();

for (int i = 0; i < rc.size(); i++)
     std::cout << "Cluster " << rc.at(i)->getId() << ": start = " << rc.at(i)->getOverlapAtStart() << ", end = " << rc.at(i)->getOverlapAtEnd() << std::endl;

std::cout << "\n\nWith iterator:\n";

for (std::vector<RectangleCluster*>::iterator ci = p->getInnerRegionPolygons().at(0)->getClusters().begin(); ci != p->getInnerRegionPolygons().at(0)->getClusters().end(); ++ci)
    std::cout << "Cluster " << (*ci)->getId() << ": start = " << (*ci)->getOverlapAtStart() << ", end = " << (*ci)->getOverlapAtEnd() << std::endl;

控制台输出如下所示:

没有迭代器:
集群 0:开始 = 65.4238，结束 = 64.9811
集群 1:开始 = 64.9811，结束 = 17.9983
簇 2:开始 = 17.9983，结束 = 17.9983 ...

使用迭代器:
集群 34026352:开始 = 1.68113e-316，结束 = 1.68113e-316
集群 1:开始 = 64.9811，结束 = 17.9983
簇 2:开始 = 17.9983，结束 = 17.9983 ...

“...”后的输出也相等。为什么没有迭代器的代码给我“Cluster 0: start = 65.4238, end = 64.9811”而带有迭代器的代码“Cluster 34026352: start = 1.68113e-316, end = 1.68113e-316”？

最好的问候 格诺特

Answer 1

请使用迭代器重写您的代码，例如:

for (std::vector<RectangleCluster*>::iterator ci = rc.begin(); ci != rc.end(); ++ci)
    std::cout << "Cluster " << (*ci)->getId() << ": start = " << (*ci)->getOverlapAtStart() << ", end = " << (*ci)->getOverlapAtEnd() << std::endl;

我同意awoodland 的评论。很可能 p->getInnerRegionPolygons().at(0)->getClusters() 每次调用都会返回新 vector 。在 for( ... ) 运算符中比较来自不同容器的迭代器是不正确的。