Listening to Publisher in Python from C++ Subscriber: Problem

edit

tl;dr: don't create and destroy your Publishers (or Subscribers) in a tight loop, ROS won't have time to properly register your subscriptions, and the chance that your Python node publishes its message at exactly the right time (between a creation and a destruction of your Subscriber) is rather slim. Move Pub/Sub creation to your code that initialises your node, and implement your business logic in callbacks.

longer version:

while(true)
{
  sub4 = nh2.subscribe<std_msgs::Int8>("/PointCloudView", 1, saveFiles);
 [..]

This (and you probably have other lines like this elsewhere), is probably what is causing your setup not to work.

From your code, I believe you are trying to implement a polling system: retrieve the current state every so often, then upon change, influence the control flow of your program.

ROS on the other hand (and other systems implementing the Observer/Observable or Publish/Subscribe style) is a callback system: you express your interest in certain events (ie: the arrival of Int8 messages on the PointCloudView topic), tell the middleware who it should notify if/when such an event occurs (ie: you register a callback) and whenever an event occurs, the middleware will delegate processing / reacting to the event to your callback.

A typical ROS node registers its callbacks during its initialisation phase (c'tor, first part of your main, etc), initialises some internal state and then just hands over control of everything to ROS (ie: calls ros::spin()). If you have other things to do as well (so when no messages are arriving), use a loop construct and give ROS just enough time to process events every now and then (ie: call ros::spinOnce() periodically).

As to your issue: I expect that if you move the creation of your Subscriber(s) to somewhere outside your while-loop (and perhaps change some details as to how your business logic interacts with your callbacks) things will start to work.

PS: ROS does support a synchronous (ie: blocking) service based interaction style, which is similar to traditional client/server. Depending on your actual needs, that might be more suited here, but I can't say from what you've described.

Edit:

def capturePointCloud(tracker):
    pub1 = rospy.Publisher('PointCloudView', Int8, queue_size=1)
    pub1.publish(tracker)   
    print "Made it"

I'd also advise you to do the same with your Python code: right now, upon invocation of the capturePointCloud(..) function, a Publisher is created, which will try to publish a message, but it (the Publisher) will most likely only exist for a few milliseconds. I'd be surprised if it can successfully publish anything.