Seg fault on std::set integer insert

Question

I have a function that compares vectors in a vector and merges them if they are similar. I have to remember the indices of array elements that were already merged, so I save them in a queue.

On some random elements the insert of the index into the queue produces a seg fault. I really don't get why. Here is my code:

using namespace cv;
using namespace std;
//...
//...
unordered_set<uint> mergedIdxSet = unordered_set<uint>();
mergedIdxSet.reserve(regions.size());
//...
//...
cout << "Test region " << r1 << " (" << regions[r1].size() << ") with...\n";
for(uint r2 = r1+1; r2 < regions.size(); r2++)
{
    if((bBoxes[r1] & bBoxes[r2]).area() == 0)
    {
        continue;
    }

    cout << "\tRegion " << r2 << "\n";

    Rect unionBound = bBoxes[r1] | bBoxes[r2];
    Point upperLeftBound = Point(unionBound.x, unionBound.y);
    Mat interMap = Mat::zeros(unionBound.size(), CV_8UC1);
    for(uint p = 0; p < regions[r1].size(); p++)
    {
        interMap.at<uchar>(regions[r1][p]-upperLeftBound) = 128;
    }
    for(uint p = 0; p < regions[r2].size(); p++)
    {
        interMap.at<uchar>(regions[r2][p]-upperLeftBound) += 127;
    }
    int intersectionArea = countNonZero(interMap);
    if(intersectionArea / regions[r1].size() >= ratio ||
       intersectionArea / regions[r2].size() >= ratio)
    {
        cout << "\t\tMerge\n";
        mergedIdxSet.insert(r2);
        for(uint i = 0; i < regions[r2].size(); i++)
        {
            pointSet.insert(regions[r2][i]);
        }
        regions[r1] = vector<Point>(pointSet.begin(), pointSet.end());
        cout << "New length: " << regions[r1].size() << "\n";
    }
}

The algorithm begins with region 0 and merges regions 1, 2, 3, 4, 5, 6 and 8. Then it wants to merge region 685 and crashes upon adding the unsigned int 685 in variable r2 into mergedIdxSet. If I just skip the insert it crashes when trying to insert regions[r2] into pointSet. If I skip the region 685 it crashes on some other region much later. Why does that happen?

Thanks in advance.

Answer 1

The problem was that I tried to overwrite the vector in regions[r1]. Somehow that caused the whole program to crash at the queue insert. I replaced the merging process by deleting the very similar regions and it works now.

Thanks for the input.