前面我们定义了发布者和订阅者，里面的消息格式都是已经定义好了的，这里介绍怎么自定义我们自己的消息格式

1. 定义消息

1.1. 定义msg文件

ros中，定义消息是语言无关的，定义消息文件保存在如下

catkin_ws/src/learning_topic/msg/Person.msg

Person.msg 文件就是我们的消息文件，后缀为msg，语言无关，内容如下

//字符串 名称
string name
//uint8 性别
uint8 sex
// uint8 年龄
uint8 age

//这种方式定义性别枚举
uint8 unknown = 0
uint8 male = 1
uint8 female = 2

1.2. 在package.xml中添加功能包依赖

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

1.3. 在CMakeList.txt添加编译选项

在 find_package 语句后面追加 message_generation

find_package(catkin REQUIRED COMPONENTS
  ....
  message_generation
)

在 add_message_files 后面追加 Person.msg

add_message_files(
  FILES
  Person.msg
)

在 generate_messages 后面追加 std_msgs

generate_messages(
  DEPENDENCIES
  std_msgs
)

在 catkin_package后面追加 message_runtime

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

1.4. 编译

cd catkin_ws
catkin_make

2.定义发布者和订阅者

2.1 定义发布者

catkin_ws/src/learning_topic/src/person_publisher.cpp

内容如下

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

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

    ros::NodeHandle node;

    // 创建一个publisher 发布名为/person_info的主题，消息类型为learning_topic::Person, 队列长度为10
    ros::Publisher person_info_pub = node.advertise<learning_topic::Person>("/person_info", 10);

    ros::Rate loop_rate(1);
    int count = 0;

    while (ros::ok())
    {
        learning_topic::Person person_msg;
        person_msg.name = "Tom";
        person_msg.age = 18;
        person_msg.sex = learning_topic::Person::male;

        // 发布消息
        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);

        loop_rate.sleep();
    }

    return 0;
}

2.2. 定义订阅者

catkin_ws/src/learning_topic/src/person_subscriber.cpp

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

void person_info_callback(const learning_topic::Person::ConstPtr &msg)
{
    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)
{
    ros::init(argc, argv, "person_subscriber");

    ros::NodeHandle node;

    ros::Subscriber person_info_sub = node.subscribe("/person_info", 10, person_info_callback);

    ros::spin();

    return 0;
}

2.3. 修改CMakeList.txt

catkin_ws/src/learning_topic/CMakeLists.txt

添加

add_executable(person_publisher src/person_publisher.cpp)
add_executable(person_subscriber src/person_subscriber.cpp)

add_dependencies(person_publisher ${PROJECT_NAME}_generate_messages_cpp)
add_dependencies(person_subscriber ${PROJECT_NAME}_generate_messages_cpp)

target_link_libraries(person_publisher
  ${catkin_LIBRARIES}
)
target_link_libraries(person_subscriber
  ${catkin_LIBRARIES}
)

2.4 编译

cd catkin_ws
catkin_make

3. 使用消息

3.1 启动ros主程序

roscore

3.2. 启动发布者

另开一个终端

source devel/setup.sh
rosrun learning_topic person_publisher 

3.3 启动订阅者

source devel/setup.sh
rosrun learning_topic person_subscriber