Following error occured when compiling custom message in ROS

Question

I'm following "WS Newman's" tutorial on how to create ROS custom message. Following error occured when compiling "The dependencies of the message/service 'example_msg/Num' have changed. Please rerun cmake"

Num.msg has

Header header
int32 demo_int
float64 demo_double

Cmakelists.txt

project(example_msg)

find_package(catkin REQUIRED COMPONENTS
  roscpp
  std_msgs
  message_generation
)
add_message_files(
   FILES
   Num.msg
#   Message2.msg
)
generate_messages(
 DEPENDENCIES
 std_msgs
 )
catkin_package(

CATKIN_DEPENDS message_runtime
)
include_directories(
  include ${catkin_INCLUDE_DIRS}
# include
  ${catkin_INCLUDE_DIRS}
)
add_executable(example_ros_message_publisher
  src/example_ros_message_publisher.cpp
)
add_dependencies(example_ros_message_publisher ${${PROJECT_NAME}_EXPORTED_TARGETS} ${catkin_EXPORTED_TARGETS})
target_link_libraries(example_ros_message_publisher
  ${catkin_LIBRARIES}
)

package.xml

<package format="2">
  <name>example_msg</name>
  <version>0.0.0</version>
  <description>The example_msg package</description>
    <maintainer email="asiri@todo.todo">asiri</maintainer>
  <license>TODO</license>
    <build_depend>message_generation</build_depend>
     <exec_depend>message_runtime</exec_depend> 
   <buildtool_depend>catkin</buildtool_depend>
  <build_depend>roscpp</build_depend>
  <build_depend>std_msgs</build_depend>
  <build_export_depend>roscpp</build_export_depend>
  <build_export_depend>std_msgs</build_export_depend>
  <exec_depend>roscpp</exec_depend>
  <exec_depend>std_msgs</exec_depend>
  <export>
     </export>
</package>

example_ros_message_publisher.cpp

#include <ros/ros.h>
#include <example_msg/Num.h>
#include <math.h>

int main(int argc, char **argv) {
    ros::init(argc, argv, "example_ros_message_publisher"); // name of this node 
    ros::NodeHandle n; // two lines to create a publisher object that can talk to ROS
    ros::Publisher my_publisher_object = n.advertise<example_msg::Num>("example_topic", 1);
    //"example_topic" is the name of the topic to which we will publish
    // the "1" argument says to use a buffer size of 1; could make larger, if expect network backups

    example_msg::Num  my_new_message;
    //create a variable of type "example_msg", 
    // as defined in this package

   ros::Rate naptime(1.0); //create a ros object from the ros “Rate” class; 
   //set the sleep timer for 1Hz repetition rate (arg is in units of Hz)

   // put some data in the header.  Do: rosmsg show std_msgs/Header
   //  to see the definition of "Header" in std_msgs
    my_new_message.header.stamp = ros::Time::now(); //set the time stamp in the header;
    my_new_message.header.seq=0; // call this sequence number zero
    my_new_message.header.frame_id = "base_frame"; // would want to put true reference frame name here, if needed for coord transforms
    my_new_message.demo_int= 1;
    my_new_message.demo_double=100.0;

    double sqrt_arg;
    // do work here in infinite loop (desired for this example), but terminate if detect ROS has faulted
    while (ros::ok()) 
    {
       my_new_message.header.seq++; //increment the sequence counter
       my_new_message.header.stamp = ros::Time::now(); //update the time stamp
       my_new_message.demo_int*=2.0; //double the integer in this field
       sqrt_arg = my_new_message.demo_double;
       my_new_message.demo_double = sqrt(sqrt_arg);

        my_publisher_object.publish(my_new_message); // publish the data in new message format on topic "example_topic"
    //the next line will cause the loop to sleep for the balance of the desired period 
        // to achieve the specified loop frequency 
    naptime.sleep(); 
    }
}

When i run catkin_make install following error appear. "The dependencies of the message/service 'example_msg/Num' have changed. Please rerun cmake."

Answer 1

A bug in catkin. To trigger a deeper level of rebuild, you can touch the CMakeLists.txt file of the package that contains your example_msg/Num.