Hello world 1 - RTT Tutorial: Task execution

The source code of this tutorial can be found in the GitHub repository.

It is recommended to read Creating a Basic Component and Task Application Code before starting this tutorial.

In this tutorial a component of type Hello will be created, you can find the code in the HelloWorld.cpp file:

* @file HelloWorld.cpp
* This file demonstratess the Orocos TaskContext execution with
* a 'hello world' example.

#include <rtt/RTT.hpp>
#include <rtt/Component.hpp>

using namespace std;
using namespace Orocos;

namespace Example

    * Every component inherits from the 'RTT::TaskContext' class.  This base
    * class allow a user to add a primitive to the interface and contains
    * an ExecutionEngine which executes the application code.
    class Hello
        : public RTT::TaskContext
        * This example sets the interface up in the Constructor
        * of the component.
        Hello(std::string name)
            : RTT::TaskContext(name)

        void updateHook()
          RTT::log(Info) << "Update !" << RTT::endlog();

        bool configureHook()
          log(Info) << "Configure !" <<endlog();
          return true;

        bool startHook()
          log(Info) << "Start !" <<endlog();
          return this->getPeriod() == 0.5;

        void stopHook()
          log(Info) << "Stop !" <<endlog();

        void cleanupHook()
          log(Info) << "Cleanup !" <<endlog();



Tutorial 1


This tutorial assumes that you have installed Orocos through the pre-compiled packages distributed via ROS in Ubuntu. If you don’t have it installed, try following the instructions from Installation options.

First, compile the application as shown below.


ROS is not needed to run Orocos or to follow this tutorial, but it is a convenient way to quickly get started.

# You can change the next two settings in accordance to your setup
export RTT_TUTORIALS_WS=${HOME}/orocos_tutorials_ws
export ROS_DISTRO=kinetic

# Get the repository with the exercises on place
mkdir -p ${RTT_TUTORIALS_WS}/src
git clone https://github.com/orocos-toolchain/rtt_examples.git
cd ..

# Build the examples using ROS catkin tools
source /opt/ros/${ROS_DISTRO}/setup.bash
catkin build

All components inherit from RTT::TaskContext, which provides the ExecutionEngine which executes the application code. You can add your application code in the respective *Hook methods. The component must be registered using the ORO_CREATE_COMPONENT macro.

Let’s see how this works in practice. The start.ops file used to deploy this component looks like:



The import statement just imports the package, the loadComponent instantiates the component Example::Hello with name hello (this is the std::string name passed to the constructor of RTT::TaskContext).

You can run it this way:

source ${RTT_TUTORIALS_WS}/devel/setup.bash
deployer-gnulinux -lInfo -s $(rospack find hello_1_task_execution)/start.ops

Now you should have the interface of the Orocos deployer that allows to input Orocos scripting language commands.


In order to find out which functions this component has, type ls, and for detailed information, type help this (i.e. print the interface of the ‘this’ task object).

We can then configure our component (invoke the configureHook function):


In this example the period of the is set in the configureHook method.

Next we can start our component:


This will call the startHook function of our component, if that returns true, the updateHook function will be executed, at the rate defined by the period that was set in configureHook. In this example, startHook only returns true if the period is set to 0.5. Try to set this to a different value in updateHook and see what happens when you try to start the application.


By default a component starts in the Stopped state (see Task Application Code), which makes the configure call optional. You can make the configure call required by specifying the state of the TaskContext in the constructor of your component:

Hello(std::string name)
    : RTT::TaskContext(name, PreOperational)

The stopHook and cleanupHook can also be invoked from the Orocos deployer: