icp setIndices doesn't work

pcl::PointCloud<pcl::PointXYZ>::Ptr cloud_in (new pcl::PointCloud<pcl::PointXYZ>);
    pcl::PointCloud<pcl::PointXYZ>::Ptr cloud_out (new pcl::PointCloud<pcl::PointXYZ>);

    // Fill in the CloudIn data
    cloud_in->width    = 1000;
    cloud_in->height   = 1;
    cloud_in->is_dense = false;
    cloud_in->points.resize (cloud_in->width * cloud_in->height);
    for (size_t i = 0; i < cloud_in->points.size (); ++i)
    {
        cloud_in->points[i].x = 1024 * rand () / (RAND_MAX + 1.0f);
        cloud_in->points[i].y = 1024 * rand () / (RAND_MAX + 1.0f);
        cloud_in->points[i].z = 1024 * rand () / (RAND_MAX + 1.0f);
    }

    cloud_out->width    = 100;
    cloud_out->height   = 1;
    cloud_out->is_dense = false;
    cloud_out->points.resize (cloud_out->width * cloud_out->height);

    for (size_t i = 0; i < cloud_out->points.size (); ++i)
    {
        cloud_out->points[i].x = cloud_in->points[i].x + 0.7f;
        cloud_out->points[i].y = cloud_in->points[i].y;
        cloud_out->points[i].z = cloud_in->points[i].z;
    }
    std::cout << cloud_out->points.size() << std::endl;


    boost::shared_ptr< std::vector<int> > pr(new std::vector<int>);
   // first try
   //   for(int i=0; i<100; i+=1)
    //    pr->push_back(i);
 // second try
    for(int i=100; i<200; i+=1)
        pr->push_back(i);

    pcl::IterativeClosestPoint<pcl::PointXYZ, pcl::PointXYZ> icp;
    icp.setMaxCorrespondenceDistance(0.5);
    icp.setTransformationEpsilon(1e-12);
    icp.setEuclideanFitnessEpsilon(0.0001);
    icp.setMaximumIterations (1000000);
    icp.setInputSource(cloud_in);
    icp.setInputTarget(cloud_out);

    //icp.setIndices(pr);
    pcl::PointCloud<pcl::PointXYZ> Final;
    icp.align(Final);

    std::cout << "has converged:" << icp.hasConverged() << " score: " <<
              icp.getFitnessScore() << std::endl;

    std::cout << icp.getFinalTransformation() << std::endl;

    pcl::transformPointCloud(*cloud_out,*cloud_out,icp.getFinalTransformation().inverse());