文章目錄

• 1.編寫發布者節點
• 2. 編寫訂閱者節點
• 3.構建節點
• 4.運行節點

1.編寫發布者節點

在之前創建的study/src目錄下創建talker.cpp文件并粘貼以下內容進去

#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) {/*** The ros::init() function needs to see argc and argv so that it can perform* any ROS arguments and name remapping that were provided at the command line.* For programmatic remappings you can use a different version of init() which takes* remappings directly, but for most command-line programs, passing argc and argv is* the easiest way to do it. The third argument to init() is the name of the node.** You must call one of the versions of ros::init() before using any other* part of the ROS system.*/ros::init(argc, argv, "talker");/*** NodeHandle is the main access point to communications with the ROS system.* The first NodeHandle constructed will fully initialize this node, and the last* NodeHandle destructed will close down the node.*/ros::NodeHandle n;/*** The advertise() function is how you tell ROS that you want to* publish on a given topic name. This invokes a call to the ROS* master node, which keeps a registry of who is publishing and who* is subscribing. After this advertise() call is made, the master* node will notify anyone who is trying to subscribe to this topic name,* and they will in turn negotiate a peer-to-peer connection with this* node. advertise() returns a Publisher object which allows you to* publish messages on that topic through a call to publish(). Once* all copies of the returned Publisher object are destroyed, the topic* will be automatically unadvertised.** The second parameter to advertise() is the size of the message queue* used for publishing messages. If messages are published more quickly* than we can send them, the number here specifies how many messages to* buffer up before throwing some away.*/ros::Publisher chatter_pub = n.advertise<std_msgs::String>("chatter", 1000);ros::Rate loop_rate(10);/*** A count of how many messages we have sent. This is used to create* a unique string for each message.*/int count = 0;while (ros::ok()){/*** This is a message object. You stuff it with data, and then publish it.*/std_msgs::String msg;std::stringstream ss;ss << "hello world " << count;msg.data = ss.str();ROS_INFO("%s", msg.data.c_str());/*** The publish() function is how you send messages. The parameter* is the message object. The type of this object must agree with the type* given as a template parameter to the advertise<>() call, as was done* in the constructor above.*/chatter_pub.publish(msg);ros::spinOnce();loop_rate.sleep();++count;}return 0; }

這部分代碼的解讀，可參考：添加鏈接描述

2. 編寫訂閱者節點

在src目錄下創建listener.cpp文件并粘貼以下內容進去：

#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) {/*** The ros::init() function needs to see argc and argv so that it can perform* any ROS arguments and name remapping that were provided at the command line.* For programmatic remappings you can use a different version of init() which takes* remappings directly, but for most command-line programs, passing argc and argv is* the easiest way to do it. The third argument to init() is the name of the node.** You must call one of the versions of ros::init() before using any other* part of the ROS system.*/ros::init(argc, argv, "listener");/*** NodeHandle is the main access point to communications with the ROS system.* The first NodeHandle constructed will fully initialize this node, and the last* NodeHandle destructed will close down the node.*/ros::NodeHandle n;/*** The subscribe() call is how you tell ROS that you want to receive messages* on a given topic. This invokes a call to the ROS* master node, which keeps a registry of who is publishing and who* is subscribing. Messages are passed to a callback function, here* called chatterCallback. subscribe() returns a Subscriber object that you* must hold on to until you want to unsubscribe. When all copies of the Subscriber* object go out of scope, this callback will automatically be unsubscribed from* this topic.** The second parameter to the subscribe() function is the size of the message* queue. If messages are arriving faster than they are being processed, this* is the number of messages that will be buffered up before beginning to throw* away the oldest ones.*/ros::Subscriber sub = n.subscribe("chatter", 1000, chatterCallback);/*** ros::spin() will enter a loop, pumping callbacks. With this version, all* callbacks will be called from within this thread (the main one). ros::spin()* will exit when Ctrl-C is pressed, or the node is shutdown by the master.*/ros::spin();return 0; }

3.構建節點

前面的介紹使用了catkin_create_pkg，它創建了一個和一個package.xml和CMakeLists.txt文件。只需將這幾行添加到CMakeLists.txt文件的底部：

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

這將創建兩個可執行文件talker和listener，默認情況下，它們將被放到軟件包目錄下的devel空間中，即~/catkin_ws/devel/lib/。

現在可以運行catkin_make：

# 在你的catkin工作空間下 $ cd ~/catkin_ws $ catkin_make

4.運行節點

打開一個終端，運行roscore；
再打開一個新的終端，運行接收節點：rosrun study listener
再打開一個新的終端，運行發布節點：rosrun study talker
再打開一個新的終端，運行rqt_graph，可以看到：

總結

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