How to get the name or id of a pcl_visualizer

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I need to get the name or id of a pcl::visulization::PCLvisualizer because I need to show three visualizers at the same time for comparision and I use a set of shortcuts to save them. My C++ code is as follows(I have marked the place where the code needs to be added)and I'm very appreciated for your help.

#include <pcl/visualization/pcl_visualizer.h>
void keyboardEventOccurred (const pcl::visualization::KeyboardEvent &event,
                            void* viewer_void)
{
  pcl::visualization::PCLVisualizer *viewer = static_cast<pcl::visualization::PCLVisualizer *> (viewer_void);
  std::string saved_name = "/home/ouni/Code/pcl_test/" ;
  if (event.getKeySym () == "s" && event.keyDown () && event.isCtrlPressed()) // Ctrl+S -> save the screen shot
  {
    std::cout << "Ctrl + S was pressed => saving screen shot..." << std::endl;
    //saved_name += *********************add code here***************************
    viewer->saveScreenshot(saved_name);
    std::cout << "screen shot saved!" << std::endl;
  }
}
pcl::visualization::PCLVisualizer::Ptr
DrawPC(const pcl::PointCloud<pcl::PointXYZ>::Ptr cloud_ptr, std::string viewer_name="3D Viewer") {
  pcl::visualization::PCLVisualizer::Ptr viewer(
      new pcl::visualization::PCLVisualizer(viewer_name));
  viewer->setBackgroundColor(0, 0, 0);
  pcl::visualization::PointCloudColorHandlerCustom<pcl::PointXYZ> single_color(
      cloud_ptr, 255, 255, 255);
  viewer->addPointCloud<pcl::PointXYZ>(cloud_ptr, single_color, "total PC");
  viewer->setPointCloudRenderingProperties(
      pcl::visualization::PCL_VISUALIZER_POINT_SIZE, 3, "total PC");
  viewer->addCoordinateSystem(1.0);
  viewer->initCameraParameters();
  viewer->registerKeyboardCallback (keyboardEventOccurred, (void*)viewer.get ());
  return (viewer);
}
...
int main(){
 viewer1 = DrawPC(cloud, "initial_points"); // **set window name here,but how to get it?**
 while(!viewer1->wasStopped()){
   viewer1->spinOnce(100);
 }
}