五、话题编程

一、话题编程

1、创建talker.cpp

#include <sstream>					
#include "ros/ros.h"
#include "std_msgs/String.h"

int main(int argc, char **argv)
{
  // ROS节点初始化
  ros::init(argc, argv, "talker");  //这里的前两个参数和main函数的参数一样，最后一个参数就是节点的talker

  // 创建节点句柄，一种特殊的指针
  ros::NodeHandle n;

  // 创建一个Publisher，发布名为chatter的topic，消息类型为std_msgs::String
  ros::Publisher chatter_pub = n.advertise<std_msgs::String>("chatter", 1000);//发布者存放的队列最大长度，超出后，前面的被删除

  // 设置循环的频率
  ros::Rate loop_rate(10);

  int count = 0;
  while (ros::ok())
  {
        // 初始化std_msgs::String类型的消息
    std_msgs::String msg;
    std::stringstream ss;
    ss << "hello world " << count;
    msg.data = ss.str();

        // 发布消息
    ROS_INFO("%s", msg.data.c_str());
    chatter_pub.publish(msg);

        // 循环等待回调函数
    ros::spinOnce();

        // 按照循环频率延时，减少cpu占用
    loop_rate.sleep();
    ++count;
  }

  return 0;
} 

2、创建listener.cpp

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

// 接收到订阅的消息后，会进入消息回调函数
void chatterCallback(const std_msgs::String::ConstPtr& msg)
{
  // 将接收到的消息打印出来
  ROS_INFO("I heard: [%s]", msg->data.c_str());
}

int main(int argc, char **argv)
{
  // 初始化ROS节点
  ros::init(argc, argv, "listener");

  // 创建节点句柄
  ros::NodeHandle n;

  // 创建一个Subscriber，订阅名为chatter的topic，注册回调函数chatterCallback
  ros::Subscriber sub = n.subscribe("chatter", 1000, chatterCallback);//毁掉函数机制，当收到订阅的消息时，就会进入回调函数

  // 循环等待回调函数
  ros::spin();//

  return 0;
}

3、编译

（1）打开功能包下面的CMakelists.txt,找到 build，加入如下代码

add_executable(talker src/talker.cpp)  //添加生成相应节点所依赖的代码快，不止一个
target_link_libraries(talker ${catkin_LIBRARIES})
#add_dependencies(talker ${PROJECT_NAME}_generate_messages_cpp)

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

add_executable(server src/server.cpp)
target_link_libraries(server ${catkin_LIBRARIES})
add_dependencies(server ${PROJECT_NAME}_gencpp)

add_executable(client src/client.cpp)
target_link_libraries(client ${catkin_LIBRARIES})
add_dependencies(client ${PROJECT_NAME}_gencpp)

add_executable(DoDishes_client src/DoDishes_client.cpp)
target_link_libraries( DoDishes_client ${catkin_LIBRARIES})
add_dependencies(DoDishes_client ${${PROJECT_NAME}_EXPORTED_TARGETS})

add_executable(DoDishes_server src/DoDishes_server.cpp)
target_link_libraries( DoDishes_server ${catkin_LIBRARIES})
add_dependencies(DoDishes_server ${${PROJECT_NAME}_EXPORTED_TARGETS})

（2) 回到工作空间下(catkin_ws)，进行编译
catkin_make

4、运行

	（1）roscore
	  (2)  rosrun  learning_communication talker
	  (3)  rosrun  learning_communication listener