检查向量索引是否为空 [英] check to see if vector index is empty
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问题描述
在我的代码中，我需要这样做:
In my code, I need to do this:
if (edges[j].ConnectedToNode() != i) //problem line
{
edges.push_back(Edge(i, j, nodes[i].Position(), nodes[j].Position(), distanceToNode));
}
然而，edge[j] 可能还不存在.如何对此进行测试以避免和索引超出范围的异常?(这与路径节点有关，本质上如果有一条边将 j 连接到 i，我不想在 i 到 j 之间添加另一个边.
however, there is a possibility that edges[j] does not exist yet. how can I test for this to avoid and index out-of-range exception? (This is to do with path nodes, essentially if there is an edge connecting j to i, I don't want to add another from i to j.
推荐答案
在访问 edges[j] 之前检查 j
Before accessing edges[j] check that j < edges.size().
为了说明 Mark Ransom 的评论:
To illustrate what Mark Ransom commented:
if (j < edges.size() && edges[j].ConnectedToNode() != i) //problem line
{
edges.push_back(Edge(i, j, nodes[i].Position(), nodes[j].Position(), distanceToNode));
}
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