ROS简单的发布器节点和订阅器节点

发布器节点的操作步骤：
1、初始化ROS系统
2、在ROS网络内广播我们将要在chatter topic上发布xxx消息
3、以某种频率在chatter上发布消息
订阅器节点的操作步骤：
1、初始化ROS系统
2、订阅chatter topic
3、进入自循环，等待消息的到达
4、当消息到达，调用chatterCallback()函数

创建消息（msg）
1、在catkin_ws/src/beginner_tutorials目录下创建msg/Num.msg文件
2、然后在package.xml文件中添加

<build_depend>message_generationbuild_depend>
<run_depend>message_runtimerun_depend>

3、在CMakeLists.txt文件中利用find_package函数，增加对message_generation的依赖，这样就可以生成消息了，你可以直接在COMPONENTS的列表里增加message_generation，就像这样：

# Do not just add this line to your CMakeLists.txt, modify the existing line
find_package(catkin REQUIRED COMPONENTS roscpp rospy std_msgs message_generation)

4、同样，你需要确保你设置了运行依赖

catkin_package(
  ...
  CATKIN_DEPENDS message_runtime ...
  ...)

5、添加

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

6、在CMakefiles.txt的最后一行添加

add_executable(talker src/talker.cpp)
target_link_libraries(talker ${catkin_LIBRARIES})
add_dependencies(talker beginner_tutorials_generate_messages_cpp)

add_executable(listener src/listener.cpp)
target_link_libraries(listener ${catkin_LIBRARIES})
add_dependencies(listener beginner_tutorials_generate_messages_cpp)

7、然后在beginner_tutorials/src目录下添加两个cpp文件
listener.cpp

#include "ros/ros.h"
#include "std_msgs/String.h"

/**
 * This tutorial demonstrates simple receipt of messages over the ROS system.
 */
void chatterCallback(const std_msgs::String::ConstPtr& msg)
{
  ROS_INFO("I heard: [%s]", msg->data.c_str());
}

int main(int argc, char **argv)
{

  ros::init(argc, argv, "listener");

  ros::NodeHandle n;

  ros::Subscriber sub = n.subscribe("chatter", 1000, chatterCallback);

  ros::spin();

  return 0;
}

talker.cpp

#include "ros/ros.h"  //
#include "std_msgs/String.h"

#include <sstream>

/**
 * This tutorial demonstrates simple sending of messages over the ROS system.
 */
int main(int argc, char **argv)
{

  ros::init(argc, argv, "talker");

  ros::NodeHandle n;

  ros::Publisher chatter_pub = n.advertise<std_msgs::String>("chatter", 1000);

  ros::Rate loop_rate(10);

  int count = 0;
  while (ros::ok())
  {

    std_msgs::String msg;

    std::stringstream ss;
    ss << "hello world " << count;
    msg.data = ss.str();

    ROS_INFO("%s", msg.data.c_str());

    chatter_pub.publish(msg);

    ros::spinOnce();

    loop_rate.sleep();
    ++count;
  }


  return 0;
}

之后就可以编译了，回到/home/meng/catkin_ws目录，执行catkin_make进行编译，注意：source devel/setup.bash
没打开一个终端都要source devel/setup.bash一下才能生效。
之后会在devel/lib/beginner_tutorials/目录下生产listener和talker俩个可执行文件
然后执行rosrun beginner_tutorials listener和rosrun beginner_tutorials talker这样就能看到一个发一个收了
注意：要先运行roscore才可以哦。
以上就是消息的发布器和订阅器。