read access violation on RTrees' getRoots getNodes getSplits methods

[smasoudn]

Please state the information for your system

• OpenCV version: 3.0 / 3.1
• Host OS: Linux (Ubuntu 14.04) / Windows 10

  In which part of the OpenCV library you got the issue?

• ml
• RTrees, DTrees

  Issue

Exception thrown for "read access violation" when using RTrees' methods. Mat.copyTo (vector) also doesn't copy the elements properly.

Code example to reproduce the issue / Steps to reproduce the issue

#include <iostream>

#include <opencv2\core\core.hpp>
#include <opencv2\highgui\highgui.hpp>
#include <opencv2\ml\ml.hpp>

using namespace std;
using namespace cv;
using namespace cv::ml;

static Ptr<TrainData> prepareTrainData(Mat& pts, Mat& classes)
{
    Mat samples;
    Mat(pts).reshape(1, (int)pts.rows).convertTo(samples, CV_32F);
    Ptr<TrainData> a = TrainData::create(samples, ROW_SAMPLE, classes);
    return a;
}

int main()
{
    Mat training = (Mat_<float>(7, 2) << 1, 1, 2, 2, 3, 3, 1, 2, 3, 4, 5, 4, 3, 2);
    Mat classes = (Mat_<int>(7, 1) << 0, 0, 0, 1, 1, 2, 2);

    cout << "training data" << endl;
    cout << endl << training << " " << endl << endl;
    cout << "classes" << endl;
    cout << endl << classes << " " << endl << endl;

    Ptr<RTrees> rtrees = RTrees::create();

    rtrees->setMaxDepth(14);
    rtrees->setMinSampleCount(2);
    rtrees->setRegressionAccuracy(0.f);
    rtrees->setUseSurrogates(false);
    rtrees->setMaxCategories(3);
    rtrees->setPriors(Mat());
    rtrees->setCalculateVarImportance(false);

    rtrees->setActiveVarCount(1);
    rtrees->setTermCriteria(TermCriteria(TermCriteria::MAX_ITER, 5, 0));
    Ptr<TrainData> a = prepareTrainData(training, classes);
    rtrees->train(a);

    // my own prediction
    vector<int> roots = rtrees->getRoots();                          // runtime error
    vector<DTrees::Node> nodes = rtrees->getNodes();    // runtime error
    vector<DTrees::Split> splits = rtrees->getSplits();        // runtime error

    Range range = Range(0, (int)roots.size());
    Mat sample = training.row(0);

    int nclasses = 2;
    vector<int> votes(nclasses, 0);
    Mat varIdx0 = a->getVarIdx();
    vector<int> varIdx;
    varIdx0.copyTo(varIdx);                                                        // wrong copy

    getchar();
    return 0;
}

[ohnozzy]

I tried the code with the latest commit 06ea0aa and did not get any runtime error. My environment: OS: WIndows 10 Compiler: VS2015

[liquidmetal]

Tried this on master commit 0330934c8bf932 and could not reproduce this.