Add loaned message listener.

Signed-off-by: Lei Liu <[email protected]>

Author: llapx

demo_nodes_cpp/CMakeLists.txt

@@ -72,6 +72,7 @@ add_library(topics_library SHARED
   src/topics/talker_loaned_message.cpp
   src/topics/talker_serialized_message.cpp
   src/topics/listener.cpp
+  src/topics/listener_loaned_message.cpp
   src/topics/listener_serialized_message.cpp
   src/topics/listener_best_effort.cpp)
 add_demo_dependencies(timers_library)
@@ -121,6 +122,9 @@ rclcpp_components_register_node(topics_library
 rclcpp_components_register_node(topics_library
   PLUGIN "demo_nodes_cpp::Listener"
   EXECUTABLE listener)
+rclcpp_components_register_node(topics_library
+  PLUGIN "demo_nodes_cpp::LoanedMessageListener"
+  EXECUTABLE listener_loaned_message)
 rclcpp_components_register_node(topics_library
   PLUGIN "demo_nodes_cpp::SerializedMessageListener"
   EXECUTABLE listener_serialized_message)

demo_nodes_cpp/src/topics/listener_loaned_message.cpp

@@ -0,0 +1,53 @@
+// Copyright 2014 Open Source Robotics Foundation, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "rclcpp/rclcpp.hpp"
+#include "rclcpp_components/register_node_macro.hpp"
+
+#include "std_msgs/msg/float64.hpp"
+#include "demo_nodes_cpp/visibility_control.h"
+
+namespace demo_nodes_cpp
+{
+  // Create a Listener class that subclasses the generic rclcpp::Node base class.
+  // The main function below will instantiate the class as a ROS node.
+  class LoanedMessageListener : public rclcpp::Node
+  {
+  public:
+    DEMO_NODES_CPP_PUBLIC
+    explicit LoanedMessageListener(const rclcpp::NodeOptions &options)
+        : Node("listener_loaned_message", options)
+    {
+      // Create a callback function for when messages are received.
+      // Variations of this function also exist using, for example UniquePtr for zero-copy transport.
+      setvbuf(stdout, NULL, _IONBF, BUFSIZ);
+      auto callback =
+          [this](const std_msgs::msg::Float64::SharedPtr msg) -> void
+      {
+        RCLCPP_INFO(this->get_logger(), "I heard: [%f]", msg->data);
+      };
+      // Create a subscription to the topic which can be matched with one or more compatible ROS
+      // publishers.
+      // Note that not all publishers on the same topic with the same type will be compatible:
+      // they must have compatible Quality of Service policies.
+      sub_ = create_subscription<std_msgs::msg::Float64>("chatter_pod", 10, callback);
+    }
+
+  private:
+    rclcpp::Subscription<std_msgs::msg::Float64>::SharedPtr sub_;
+  };
+
+} // namespace demo_nodes_cpp
+
+RCLCPP_COMPONENTS_REGISTER_NODE(demo_nodes_cpp::LoanedMessageListener)