HelloWorld Implementation Overview

ROS programming primarily uses C++ and Python. Most programs can be implemented in both languages. Each tutorial will demonstrate examples in both C++ and Python, allowing users to choose the implementation that suits them best.

The general implementation process in ROS is similar across different languages. Taking the HelloWorld program as an example, the steps are:

Create a workspace.
Create a package.
Edit source files.
Edit configuration files.
Compile and execute.

The main difference between C++ and Python lies in steps 3 and 4. The following sections detail the common steps for both implementations, with specific sections for C++ and Python.

HelloWorld (C++ Version)

Create and Initialize Workspace

bash

mkdir -p <workspace_name>/src
cd <workspace_name>
catkin_make

For example:

bash

mkdir -p seeed_ws/src
cd seeed_ws
catkin_make

Create ROS Package and Add Dependencies

bash

cd src
catkin_create_pkg <package_name> roscpp rospy std_msgs

For example:

bash

cd src
catkin_create_pkg hello_world roscpp rospy std_msgs

Edit Source File

Navigate to your package's src directory and create a new C++ source file (e.g., hello.cpp):

bash

cd ~/<workspace_name>/src/<package_name>/src
touch hello.cpp

for example:

bash

cd ~/seeed_ws/src/hello_world/src
touch hello.cpp

copy flowing code into hello.cpp:

cpp

#include "ros/ros.h"

int main(int argc, char *argv[])
{
    ros::init(argc, argv, "hello");
    ros::NodeHandle n;
    ROS_INFO("Hello World!");

    return 0;
}

Edit CMakeLists.txt

Add the following in the end of your package's CMakeLists.txt:
cmake
```
add_executable(<node_name> src/hello.cpp)
target_link_libraries(<node_name> ${catkin_LIBRARIES})
```
for example:
cmake
```
add_executable(hello src/hello.cpp)
target_link_libraries(hello ${catkin_LIBRARIES})
```
Note:The CMakeLists.txt file mentioned here is located in the created package directory, not in the workspace directory.

Compile the Workspace

bash

cd <workspace_name>
catkin_make

for example:

bash

  cd ~/seeed_ws
  catkin_make

Run the Program

Open one terminal and start ROS core:
bash
```
roscore
```
Open another terminal, source the workspace, and run the node:
bash
```
cd <workspace_name>
source devel/setup.bash
rosrun <package_name> hello
```
for example:
bash
```
cd ~/seeed_ws
source devel/setup.bash
rosrun hello_world hello
```

You should see the output: Hello World!

HelloWorld (Python Version)

Create and Initialize Workspace

bash

mkdir -p <workspace_name>/src
cd <workspace_name>
catkin_make

For example:

bash

mkdir -p seeed_ws/src
cd seeed_ws
catkin_make

Create ROS Package and Add Dependencies

bash

cd src
catkin_create_pkg <package_name> roscpp rospy std_msgs

For example:

bash

cd src
catkin_create_pkg hello_world roscpp rospy std_msgs

Add scripts Directory and Create Python File

Navigate to your package directory, create a scripts directory, and a new Python file (e.g., hello.py):

for example:

bash

mkdir ~/seeed_ws/src/hello_world/scripts
cd ~/seeed_ws/src/hello_world/scripts
touch hello.py

python

#!/usr/bin/env python

import rospy

if __name__ == "__main__":
    rospy.init_node("hello")
    rospy.loginfo("Hello World!")

Add Executable Permissions
bash
```
sudo chmod +x hello.py
```

Edit CMakeLists.txt

Add the following in the end of your package's CMakeLists.txt:

cmake

catkin_install_python(PROGRAMS scripts/hello.py
  DESTINATION ${CATKIN_PACKAGE_BIN_DESTINATION}
)

Compile the Workspace

bash

cd <workspace_name>
catkin_make

for example:

bash

cd ~/seeed_ws
catkin_make

Run the Program Open one terminal and start ROS core:
bash
```
roscore
```
Open another terminal, source the workspace, and run the node:
bash
```
cd <workspace_name>
source devel/setup.bash
rosrun <package_name> hello.py
```
For example:
bash
```
cd ~/seeed_ws
source devel/setup.bash
rosrun hello_world hello.py
```
You should see the output: Hello World!

Note

To make sourcing the workspace setup file more convenient, add it to your .bashrc:

bash

echo "source ~/<workspace_name>/devel/setup.bash" >> ~/.bashrc

This ensures that the workspace is sourced automatically whenever a new terminal is opened.