The first program in the publish/subscribe example, topic_publisher.cpp, defines two new functions: one that publishes messages to the topic exchange, and one that indicates that no more messages are coming.

The publish_messages() function publishes a series of five messages using the specified routing key.

void publish_messages(Session& session, string routing_key)
{
  Message message;

  // Set the routing key once, we'll use the same routing key for all
  // messages.

  message.getDeliveryProperties().setRoutingKey(routing_key); 
  for (int i=0; i<5; i++) {
    stringstream message_data;
    message_data << "Message " << i;

    message.setData(message_data.str());
    session.messageTransfer(arg::content=message, arg::destination="amq.topic");
  }
}

The no_more_messages() function signals the end of messages using the control routing key, which is reserved for control messages.

void no_more_messages(Session& session)
{
  Message message;

  message.getDeliveryProperties().setRoutingKey("control"); 
  message.setData("That's all, folks!");
  session.messageTransfer(arg::content=message, arg::destination="amq.topic");
}

In the main body of the program, messages are published using four different routing keys, and then the end of messages is indicated by a message sent to a separate routing key.

    publish_messages(session, "usa.news");
    publish_messages(session, "usa.weather");
    publish_messages(session, "europe.news");
    publish_messages(session, "europe.weather");
    
    no_more_messages(session);