I have created a node which reads array of integers from a file and publishes over Topic_1 at once

...
 ros::Publisher publisher = nh.advertise<std_msgs::Int32MultiArray>("Topic_1",1000,true);


  std_msgs::Int32MultiArray vec;


  ROS_INFO("Array elements from file [array1.txt] are published to Topic_1:\n");
  ifstream infile("array1.txt");

  while(infile >> temp)
      vec.data.push_back(temp);

  publisher.publish(vec);
  ros::spin();
...

and here is the subscriber for Topic_1

void callback_1(const std_msgs::Int32MultiArray::ConstPtr& vec1)
{ 
  ROS_INFO("Vector recieved over Topic_1\n");
  vector<int>::const_iterator itr = vec1->data.begin();

  for(;itr != vec1->data.end();++itr)
    {
      ROS_INFO("%d ",*itr);
    }
}
...
ros::Subscriber sub_1 = nh.subscribe("Topic_1",1000,callback_1);
...

There are no errors when I compile these nodes. But when I launch these nodes using roslaunch, 'for' loop in callback_1 is not at all executed.

 ROS_INFO("Vector recieved over Topic_1\n"); is executed

What could probably be going wrong?

for(auto const& dt: vec1->data)
{
  ROS_INFO("%d ",dt);
}