学习10：消息发布器和订阅器(C++)

因为我不会python，所以只能用C++了  - -#

1 节点

ROS中把可执行文件叫做【节点】。

去刚才的beginner_tutorial（眼花了，单词打没打错？……）目录下，新建src文件夹，里面写一个

talker.cpp

里面代码如下

/* * Copyright (C) 2008, Morgan Quigley and Willow Garage, Inc. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions are met: *   * Redistributions of source code must retain the above copyright notice, *     this list of conditions and the following disclaimer. *   * Redistributions in binary form must reproduce the above copyright *     notice, this list of conditions and the following disclaimer in the *     documentation and/or other materials provided with the distribution. *   * Neither the names of Stanford University or Willow Garage, Inc. nor the names of its *     contributors may be used to endorse or promote products derived from *     this software without specific prior written permission. * * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE * POSSIBILITY OF SUCH DAMAGE. */// %Tag(FULLTEXT)%// %Tag(ROS_HEADER)%#include "ros/ros.h"// %EndTag(ROS_HEADER)%// %Tag(MSG_HEADER)%#include "std_msgs/String.h"// %EndTag(MSG_HEADER)%#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.   */// %Tag(INIT)%  ros::init(argc, argv, "talker");// %EndTag(INIT)%  /**   * 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.   */// %Tag(NODEHANDLE)%  ros::NodeHandle n;// %EndTag(NODEHANDLE)%  /**   * 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.   */// %Tag(PUBLISHER)%  ros::Publisher chatter_pub = n.advertise<std_msgs::String>("chatter", 1000);// %EndTag(PUBLISHER)%// %Tag(LOOP_RATE)%  ros::Rate loop_rate(10);// %EndTag(LOOP_RATE)%  /**   * A count of how many messages we have sent. This is used to create   * a unique string for each message.   */// %Tag(ROS_OK)%  int count = 0;  while (ros::ok())  {// %EndTag(ROS_OK)%    /**     * This is a message object. You stuff it with data, and then publish it.     */// %Tag(FILL_MESSAGE)%    std_msgs::String msg;    std::stringstream ss;    ss << "hello world " << count;    msg.data = ss.str();// %EndTag(FILL_MESSAGE)%// %Tag(ROSCONSOLE)%    ROS_INFO("%s", msg.data.c_str());// %EndTag(ROSCONSOLE)%    /**     * 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.     */// %Tag(PUBLISH)%    chatter_pub.publish(msg);// %EndTag(PUBLISH)%// %Tag(SPINONCE)%    ros::spinOnce();// %EndTag(SPINONCE)%// %Tag(RATE_SLEEP)%    loop_rate.sleep();// %EndTag(RATE_SLEEP)%    ++count;  }  return 0;}// %EndTag(FULLTEXT)%

再新建一个listener.cpp文件，代码如下

/* * Copyright (C) 2008, Morgan Quigley and Willow Garage, Inc. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions are met: *   * Redistributions of source code must retain the above copyright notice, *     this list of conditions and the following disclaimer. *   * Redistributions in binary form must reproduce the above copyright *     notice, this list of conditions and the following disclaimer in the *     documentation and/or other materials provided with the distribution. *   * Neither the names of Stanford University or Willow Garage, Inc. nor the names of its *     contributors may be used to endorse or promote products derived from *     this software without specific prior written permission. * * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE * POSSIBILITY OF SUCH DAMAGE. */// %Tag(FULLTEXT)%#include "ros/ros.h"#include "std_msgs/String.h"/** * This tutorial demonstrates simple receipt of messages over the ROS system. */// %Tag(CALLBACK)%void chatterCallback(const std_msgs::String::ConstPtr& msg){  ROS_INFO("I heard: [%s]", msg->data.c_str());}// %EndTag(CALLBACK)%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.   */// %Tag(SUBSCRIBER)%  ros::Subscriber sub = n.subscribe("chatter", 1000, chatterCallback);// %EndTag(SUBSCRIBER)%  /**   * 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.   */// %Tag(SPIN)%  ros::spin();// %EndTag(SPIN)%  return 0;}// %EndTag(FULLTEXT)%

2 编译节点

写好了代码自然要编译把- -#

再CMakeList.txt加入

include_directories(include ${catkin_INCLUDE_DIRS})add_executable(talker src/talker.cpp)target_link_libraries(talker ${catkin_LIBRARIES})add_executable(listener src/listener.cpp)target_link_libraries(listener ${catkin_LIBRARIES})

这会生成2个可执行文件talker和listener。并且存储cakin_ws/devel/lib/<package name>里。

还需要一行

add_dependencies(talker beginner_tutorials_generate_messages_cpp)

好了好了！！！先试试能不能编译通过，然后再研究代码的意思！

回到最高的工作空间，执行catkin_make。

生成了一堆东西，编译成功！

3. 执行节点

3.1 启动roscore

这个显然的。。先启动了先。

直接执行roscore，这个前文说过多次了

3.2 启动订阅器（listener）和发送器（talker）

首先确认source过那个我们刚在玩的工作空间下的setup,bash文件啊!!

直接

$ rosrun beginner_tutorials listener     (C++)

$ rosrun beginner_tutorials talker

字面就可以猜出来2个代码的意思~

(别忘了每个终端都需要source一次啊！！！)

4 解读代码

4.1 解读发布器代码

具体细节见代码，中文注释

#include "ros/ros.h"//貌似是核心的ros头文件，先引用了先。#include "std_msgs/String.h"//黑人问号.jpg#include <sstream>int main(int argc, char **argv){  /**   * ros::init()函数需要argc和argv，这样可以实现我们之前也做过的，重定向节点名称。   * 重定向节点名称，我们再前面小乌龟模仿移动的章节玩过了。   * 第三个参数，比如下main的"talker"貌似是默认的节点名，且不能包含奇怪字符比如/   */// %Tag(INIT)%  ros::init(argc, argv, "talker");// %EndTag(INIT)%  /**   * NodeHandle 是一个重要的节点类型，我们后续操作要用到这个东西。   * 貌似定义的时候，有很好的初始化函数。析构函数也写的很棒？   */// %Tag(NODEHANDLE)%  ros::NodeHandle n;// %EndTag(NODEHANDLE)%  /**   * advertise返回一个Publisher对象，第一个参数,"chatter"是话题名，1000是缓冲队列大小。   * （最多保存）的消息的数量。同时这个advertise还有2个功能，消息类型不对他会拒绝发布，   * 他有一个publish成员，可以用来发布消息。（后面会出现介绍）。至于。。std_msg::String   * 是干嘛的？难道指的是，发布的消息类型是std_msg::String类型的嘛？（看了源代码，貌似是这个意思）。   */// %Tag(PUBLISHER)%  ros::Publisher chatter_pub = n.advertise<std_msgs::String>("chatter", 1000);// %EndTag(PUBLISHER)%// %Tag(LOOP_RATE)%  ros::Rate loop_rate(10); //程序下面有一个ros::ok(),这个大致就是10Hz的频率执行ros::ok()// %EndTag(LOOP_RATE)%// %Tag(ROS_OK)%/** * ros::ok()为false的条件： * 1:键盘按了ctrl+c * 2:同样名字的节点被运行了 * 3：ros::shutdown() 被调用 * 4：节点中所有的 NodeHandle被销毁。 */  int count = 0;  while (ros::ok())  {// %EndTag(ROS_OK)%    /**     * This is a message object. You stuff it with data, and then publish it.     */// %Tag(FILL_MESSAGE)%    std_msgs::String msg;    std::stringstream ss;    ss << "hello world " << count;    msg.data = ss.str();// %EndTag(FILL_MESSAGE)%// %Tag(ROSCONSOLE)%    ROS_INFO("%s", msg.data.c_str()); //目测，是向终端输出字符串。// %EndTag(ROSCONSOLE)%// %Tag(PUBLISH)%    chatter_pub.publish(msg);//发布msg这个消息，msg类型正好也是之前再advertise里定义的std_msg::String类型，类型统一// %EndTag(PUBLISH)%// %Tag(SPINONCE)%    ros::spinOnce();//貌似不写这句话，回调函数就没用了// %EndTag(SPINONCE)%// %Tag(RATE_SLEEP)%    loop_rate.sleep();//上面定义了10Hz，这里就会休眠0.1s的样子。// %EndTag(RATE_SLEEP)%    ++count;  }  return 0;}// %EndTag(FULLTEXT)%

4.2 解读代码接收器

一样的，直接看代码，和代码中文注释

#include "ros/ros.h"#include "std_msgs/String.h"/** * 下面是一个回调函数。再定义接收器的时候会用到。 * 看起来接收器实现的代码内部，会自动让这个函数绑定一个 * 消息的指针。比如这里，接受的消息类型是std_msgs::String类型，和前面定义 * 的发布器发布的消息类型一样。这里抓到消息，就用ROS_INFO命令，输出到 * 终端，让我们看到。*/// %Tag(CALLBACK)%void chatterCallback(const std_msgs::String::ConstPtr& msg){  ROS_INFO("I heard: [%s]", msg->data.c_str());}// %EndTag(CALLBACK)%int main(int argc, char **argv){  ros::init(argc, argv, "listener");  ros::NodeHandle n;  /**   * 这个订阅器的代码和之前的发布其很类似，参数分别为节点名、缓存大小。   * 第三个参数和前面的回调函数应该说过了。   * 很好的析构函数保证了，对象被销毁的时候，就不会再继续订阅了。   */// %Tag(SUBSCRIBER)%  ros::Subscriber sub = n.subscribe("chatter", 1000, chatterCallback);// %EndTag(SUBSCRIBER)%  /**   * spin()函数会进入一个循环，软件实现中断程序~？中断级别之类的他怎么实现呢- -#   * 当然了，还是会接受ctrl+c之类的退出。   */// %Tag(SPIN)%  ros::spin();// %EndTag(SPIN)%  return 0;}// %EndTag(FULLTEXT)%