Adding custom .msg and .srv files

In this section, we will look at how to create custom messages and service definitions in the current package. The message definitions are stored in a .msg file, while the service definitions are stored in a .srv file. These definitions inform ROS about the type of data and the name of the data to be transmitted from a ROS node. When a custom message is added, ROS will convert the definitions into equivalent C++ codes, which we can include in our nodes.

We will start with message definitions. Message definitions must be written in the .msg file and must be kept in the msg folder, which is inside the package. We are going to create a message file called demo_msg.msg with the following definition:

string greeting 
int32 number 

So far, we have only worked with standard message definitions. Now, we have created our own definitions, which means we can learn how to use them in our code.

The first step is to edit the package.xml file of the current...