ROS入门21讲笔记（二）代码形式写一个发布者向订阅者发布消息

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mkdir myWS # 创建一个文件夹作为工作空间
mkdir -p myWS/src # 创建一个源代码空间
catkin_make # 利用catkin_make帮助我们补充剩余的空间

junwu@Room:~/Desktop/myWS$ tree -L 1
.
├── build
├── devel
└── src

3 directories, 0 files

catkin_create_pkg ask-turtlerun roscpp rospy std_msgs geometry_msgs turtlesim # 这个包名为ask-turtlerun 依赖包有roscpp rospy geometry_msgs turtlesim std_msgs

junwu@Room:~/Desktop/myWS$ tree -L 1
.
├── build
├── devel
└── src

4 directories, 0 files

.
├── CMakeLists.txt
├── include
│   └── ask-turtlerun
├── package.xml
└── src

3 directories, 2 files

#include 		           //ROS功能文件
#include           //ROS内置的信号类型支持

int main(int argc, char **argv)
{
    ros::init(argc, argv, "velocityPub"); //这个程序的节点名，将来可以在rqt_graph中看到

    ros::NodeHandle n; 		   //节点管理器句柄，这个对象可以用来发布消息

    ros::Publisher turtle_vel_pub = n.advertise("/turtle1/cmd_vel", 10); 
    					   //节点管理器调用advertise方法，向话题为"/turtle1/cmd_vel"
    					   //发布一个消息类型为geometry_msgs::Twist的消息，10表示缓冲队列长度（也就是没来得及处理的数据暂存长度）
    					   //Tips：查看消息类型 rosmsg list 查看指定消息类型详细信息 rosmsg info + xxx 
    					   //      查看话题 topic list 查看话题详细信息 ros info +xxx
    					   //返回发布者句柄，这一步相当于注册，实际发送还是要发布者发送（也就是发布者句柄）

    ros::Rate loop_rate(10); 		   //这个是ROS的sleep

    int count = 0;
    while (ros::ok())		           //如果ROS程序执行正常
    {
        geometry_msgs::Twist vel_msg;     //声明一个消息类型变量
        vel_msg.linear.x = 0.5;           //赋值
        vel_msg.angular.z = 0.2;

        turtle_vel_pub.publish(vel_msg);  //通过发布者句柄发送这个消息
        ROS_INFO("Publish turtle velocity[%0.2f ms,%0.2f rad/s]", vel_msg.linear.x, vel_msg.angular.z);
        				   //ROS_INFO就是为了格式化打印消息的
        loop_rate.sleep();	           //控制发送频率，不要太快
    }
    return 0;
}

add_executable(Demo src/main.cpp)
target_link_libraries(${catkin_LIBRARIES})

-- Build files have been written to: /home/junwu/Desktop/myWS/build
####
#### Running command: "make -j16 -l16" in "/home/junwu/Desktop/myWS/build"
####
Scanning dependencies of target Demo
[ 50%] Building CXX object ask-turtlerun/CMakeFiles/Demo.dir/src/main.cpp.o
[100%] Linking CXX executable /home/junwu/Desktop/myWS/devel/lib/ask-turtlerun/Demo
[100%] Built target Demo