1. Define msg file:
Create a new MSG folder under the catkin_ws/src/learning_topic file and a new Person.msg file under the folder.
The code in the msg file is as follows:

string name
uint8 sex
uint8 age

uint8 unknow = 0
uint8 male = 1
uint8 female = 2

2. Add functional package dependencies in package.xml:
Add in catkin_ws/src/learning_topic/package.xml

<build_depend>message_generation</build_depend>
<exec_depend>message_runtime</exec_depend>

3. Add compilation options to CMakeLists.txt:
Add message_generation to find_package, and add it as follows:

find_package(catkin REQUIRED COMPONENTS
  roscpp
  rospy
  std_msgs
  turtlesim
  message_generation
)

Add message_runtime to catkin_package, and add it as follows:

catkin_package(
#  INCLUDE_DIRS include
#  LIBRARIES learning_topic
  CATKIN_DEPENDS roscpp rospy std_msgs turtlesim message_runtime
#  DEPENDS system_lib
)

And add:

add_message_files(FILES Person.msg)
generate_messages(DEPENDENCIES std_msgs)

add_executable(person_publisher src/person_publisher.cpp)
target_link_libraries(person_publisher ${catkin_LIBRARIES})
add_dependencies(person_publisher ${PROJECT_NAME}_generate_messages_cpp)

add_executable(person_subscriber src/person_subscriber.cpp)
target_link_libraries(person_subscriber ${catkin_LIBRARIES})
add_dependencies(person_subscriber ${PROJECT_NAME}_generate_messages_cpp)

4. The code in src:
person_publisher.cpp

/**
* This routine will publish / person_info topics, customize the message type learning_topic::Person
*/

#include <ros/ros.h>
#include "learning_topic/Person.h"

int main(int argc, char **argv)
{
   // ROS Node Initialization
   ros::init(argc, argv, "person_publisher");

   // Create node handles
   ros::NodeHandle n;

   // Create a Publisher that publishes a topic named / person_info with a message type of learning_topic::Person and a queue length of 10
   ros::Publisher person_info_pub = n.advertise<learning_topic::Person>("/person_info", 10);

   // Set the frequency of the cycle
   ros::Rate loop_rate(1);

   int count = 0;
   while (ros::ok())
   {
       // Initialize learning_topic::Person-type messages
   	learning_topic::Person person_msg;
   	person_msg.name = "Tom";
   	person_msg.age  = 18;
   	person_msg.sex  = learning_topic::Person::male;

       // Publish news
   	person_info_pub.publish(person_msg);

      	ROS_INFO("Publish Person Info: name:%s  age:%d  sex:%d", 
   	 person_msg.name.c_str(), person_msg.age, person_msg.sex);

       // Delay in accordance with cyclic frequency
       loop_rate.sleep();
   }

   return 0;
}

person_subscriber.cpp

/**
* This routine subscribes to / person_info topics, customizing the message type learning_topic::Person
*/

#include <ros/ros.h>
#include "learning_topic/Person.h"

// After receiving the subscribed message, it enters the message callback function
void personInfoCallback(const learning_topic::Person::ConstPtr& msg)
{
   // Print out the received message
   ROS_INFO("Subcribe Person Info: name:%s  age:%d  sex:%d", 
   		 msg->name.c_str(), msg->age, msg->sex);
}

int main(int argc, char **argv)
{
   // Initialize ROS nodes
   ros::init(argc, argv, "person_subscriber");

   // Create node handles
   ros::NodeHandle n;

   // Create a Subscriber, subscribe to a topic named / person_info, and register the callback function personInfoCallback
   ros::Subscriber person_info_sub = n.subscribe("/person_info", 10, personInfoCallback);

   // Loop waiting callback function
   ros::spin();

   return 0;
}

5. Compile and run:
Running catkin_make in catkin_ws directory requires running the following two commands in two different terminals after compilation is completed:

Step 1 Open Receive
rosrun learning_topic person_subscriber 
Part 2 Open Send
rosrun learning_topic person_publisher