Question

I’m trying to walk through a list. Here are some declarations:

list<CG1_Edge*> ActiveEdges;
list<CG1_Edge*>::iterator ActiveEdgeIterator;

Sometimes, this code segfaults on line 2:

for (this->ActiveEdgeIterator = this->ActiveEdges.begin(); this->ActiveEdgeIterator != this->ActiveEdges.end(); ++this->ActiveEdgeIterator) {
    CG1_Edge* currentEdge = *this->ActiveEdgeIterator;
    if (currentEdge->y_up < y)
        this->ActiveEdges.erase(this->ActiveEdgeIterator);
}

Are there any common reasons why this might result in a segfault?

Answer 1

You should use something like:

for (this->ActiveEdgeIterator = this->ActiveEdges.begin(); this->ActiveEdgeIterator != this->ActiveEdges.end(); ) {
    CG1_Edge* currentEdge = *this->ActiveEdgeIterator;
    if (currentEdge->y_up < y)
        this->ActiveEdgeIterator = this->ActiveEdges.erase(this->ActiveEdgeIterator);
    else
        ++this->ActiveEdgeIterator;
}

since erase returns an iterator positionned at the next element.

(Note: having that iterator as a member looks strange.)