In this video we are going to see how to create a simple ROS Publisher in C++.

* This is a video based on the question at the ROS Answers Forum

Step 1. Create a project in ROS Development Studio(ROSDS)

ROSDS helps you follow our tutorial in a fast pace without dealing without setting up an environment locally. If you haven’t had an account yet, you can create a free account here. Let’s create a new project and call it abc_qa.

Step 2. Create a package

Let’s create a new package called abc_qa with dependency for the code.

cd catkin_ws/src
catkin_create_pkg abc_qa roscpp

Then we create a source file called abc_code.cpp under the abc_qa/src directory with the following content

int main()
{
     //Initialize and start the node
     ros::Publisher pub;
     //Define and create some messages
     abc;
     while(ros : ok)
     {
           ros_time = ros::time::now();
           pub.publish(abc);
           ros::spinOnce();               
     }

 }

In order to compile the code, we have to change the following BUILD part in the CMakeLists.txt.

...
## Declare a C++ executable
## With catkin_make all packages are built within a single CMake context
## The recommended prefix ensures that target names across packages don't collide
add_executable(abc_node src/abc_code.cpp)

## Rename C++ executable without prefix
## The above recommended prefix causes long target names, the following renames the
## target back to the shorter version for ease of user use
## e.g. "rosrun someones_pkg node" instead of "rosrun someones_pkg someones_pkg_node"
# set_target_properties(${PROJECT_NAME}_node PROPERTIES OUTPUT_NAME node PREFIX "")

## Add cmake target dependencies of the executable
## same as for the library above
add_dependencies(abc_node ${abc_node_EXPORTED_TARGETS} ${catkin_EXPORTED_TARGETS})

## Specify libraries to link a library or executable target against
target_link_libraries(abc_node
  ${catkin_LIBRARIES}
)

...

Then we can try to compile it with the following command

cd ~/catkin_ws
catkin_make

You should get several compilation errors. Let’s fix the code. It should look like this after changing.

#include <ros/ros.h>
#include <std_msgs/Int32.h>

int main(int argc, char ** argv)
{
     //Initialize and start the node
     ros::init(argc, argv, "abc");
     ros::NodeHandle nh;
     
     ros::Publisher pub = nh.advertise<std_msgs::Int32>("abc_topic", 1000);
     //Define and create some messages
     std_msgs::Int32 abc;
     abc.data = 0;
     
     ros::Rate(200);
     
     while(ros::ok)
     {
           pub.publish(abc);
           ros::spinOnce();               
     }

 }

It should work now. Try to compile and run it again with the following command

cd ~/catkin_ws
catkin_make
source devel/setup.bash
rosrun abc_qa abc_node

Now we got error said that it’s missing master now. You can either run whatever simulation from Simulations or run roscore  in a new shell to solve this problem. After launching the master, execute the code again. Although it shows nothing, it is actually starting to publish to topic /abc_topic you can see it with the command rostopic echo /abc_topic. You can also try to increment the counter in the while loop.

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