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custom_ros_msg.md

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How to Create a Custom ROS Message

In order to create a new message, Age.msg:

  1. Create a directory named msg inside your package, and there create a .msg file.
roscd <package_name>
mkdir msg
# touch message_name.msg
touch Age.msg
  1. Inside message_name.msg, and define the message types.
float32 years
float32 months
float32 days
  1. Modify CMakeLists.txt file

    • find_package()

    This is where all the packages required to COMPILE the messages of the topics, services, and actions go. In package.xml, you have to state them as build_depend.

    find_package(catkin REQUIRED COMPONENTS
    roscpp
    std_msgs
    message_generation   # Add message_generation here, after the other packages
)

    • add_message_files()

    This function includes all of the messages of this package (in the msg folder) to be compiled. The file should look like this.

    add_message_files(
    FILES
    Age.msg
)

    • generate_messages()

    Here is where the packages needed for the messages compilation are imported.

    generate_messages(
    DEPENDENCIES
    std_msgs
)

    • catkin_package()

    State here all of the packages that will be needed by someone that executes something from your package. All of the packages stated here must be in the package.xml as run_depend.

    catkin_package(
    CATKIN_DEPENDS roscpp std_msgs message_runtime   # This will NOT be the only thing here
 )
This is the minimum required for CMakeLists.txt to work:
cmake_minimum_required(VERSION 2.8.3)
project($PACKAGE_NAME$)


find_package(catkin REQUIRED COMPONENTS
  roscpp
  std_msgs
  message_generation
)

add_message_files(
  FILES
  Age.msg
)

generate_messages(
  DEPENDENCIES
  std_msgs
)

catkin_package(
  CATKIN_DEPENDS roscpp std_msgs message_runtime
)

include_directories(
  ${catkin_INCLUDE_DIRS}
)
  1. Modify package.xml file
<build_depend>message_generation</build_depend>
<run_depend>message_runtime</run_depend>
This is the minimum required for CMakeLists.txt to work:
<?xml version="1.0"?>
<package>
  <name>$PACKAGE_NAME$</name>
  <version>0.0.0</version>
  <description>The $PACKAGE_NAME$ package</description>

  <maintainer email="[email protected]">user</maintainer>

  <license>TODO</license>

 <buildtool_depend>catkin</buildtool_depend>
  <build_depend>roscpp</build_depend>
  <build_depend>std_msgs</build_depend>
  <build_depend>message_generation</build_depend>
  <run_depend>roscpp</run_depend>
  <run_depend>std_msgs</run_depend>
  <run_depend>message_runtime</run_depend>

  <export>

  </export>
</package>
  1. Compile

This executes this bash file that sets, among other things, the newly generated messages created through the catkin_make.

roscd; cd ..
catkin_make
source devel/setup.bash
  1. Use in CPP Files by adding the following to CMakeLists.txt
add_dependencies(publish_age topic_ex_generate_messages_cpp)