因為我不會python，所以只能用C++了  - -#

1 節點

ROS中把可執行檔案叫做【節點】。

去剛才的beginner_tutorial（眼花了，單詞打沒打錯？……）目錄下，新建src資料夾，裡面寫一個

talker.cpp

裡面程式碼如下

/*
 * 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)%
 

/*
 * 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)%
 

寫好了程式碼自然要編譯把- -#

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})

還需要一行

add_dependencies(talker beginner_tutorials_generate_messages_cpp)

回到最高的工作空間，執行catkin_make。

生成了一堆東西，編譯成功！

3. 執行節點

3.1 啟動roscore

這個顯然的。。先啟動了先。

直接執行roscore，這個前文說過多次了

3.2 啟動訂閱器（listener）和傳送器（talker）

首先確認source過那個我們剛在玩的工作空間下的setup,bash檔案啊!!

直接

$ rosrun beginner_tutorials listener     (C++)

$ rosrun beginner_tutorials talker

具體細節見程式碼，中文註釋

#include "ros/ros.h"
//貌似是核心的ros標頭檔案，先引用了先。

#include "std_msgs/String.h"
//黑人問號.jpg

#include <sstream>

int main(int argc, char **argv)
{
  /**
   * ros::init()函式需要argc和argv，這樣可以實現我們之前也做過的，重定向節點名稱。
   * 重定向節點名稱，我們再前面小烏龜模仿移動的章節玩過了。
   * 第三個引數，比如下main的"talker"貌似是預設的節點名，且不能包含奇怪字元比如/
   */
// %Tag(INIT)%
  ros::init(argc, argv, "talker");
// %EndTag(INIT)%

  /**
   * NodeHandle 是一個重要的節點型別，我們後續操作要用到這個東西。
   * 貌似定義的時候，有很好的初始化函式。解構函式也寫的很棒？
   */
// %Tag(NODEHANDLE)%
  ros::NodeHandle n;
// %EndTag(NODEHANDLE)%

  /**
   * advertise返回一個Publisher物件，第一個引數,"chatter"是話題名，1000是緩衝佇列大小。
   * （最多儲存）的訊息的數量。同時這個advertise還有2個功能，訊息型別不對他會拒絕釋出，
   * 他有一個publish成員，可以用來發布訊息。（後面會出現介紹）。至於。。std_msg::String
   * 是幹嘛的？難道指的是，釋出的訊息型別是std_msg::String型別的嘛？（看了原始碼，貌似是這個意思）。
   */
// %Tag(PUBLISHER)%
  ros::Publisher chatter_pub = n.advertise<std_msgs::String>("chatter", 1000);
// %EndTag(PUBLISHER)%

// %Tag(LOOP_RATE)%
  ros::Rate loop_rate(10); //程式下面有一個ros::ok(),這個大致就是10Hz的頻率執行ros::ok()
// %EndTag(LOOP_RATE)%

// %Tag(ROS_OK)%
	/**
	 * ros::ok()為false的條件：
	 * 1:鍵盤按了ctrl+c
	 * 2:同樣名字的節點被運行了
	 * 3：ros::shutdown() 被呼叫
	 * 4：節點中所有的 NodeHandle被銷燬。
	 */
  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()); //目測，是向終端輸出字串。
// %EndTag(ROSCONSOLE)%

// %Tag(PUBLISH)%
    chatter_pub.publish(msg);//釋出msg這個訊息，msg型別正好也是之前再advertise裡定義的std_msg::String型別，型別統一
// %EndTag(PUBLISH)%

// %Tag(SPINONCE)%
    ros::spinOnce();//貌似不寫這句話，回撥函式就沒用了
// %EndTag(SPINONCE)%

// %Tag(RATE_SLEEP)%
    loop_rate.sleep();//上面定義了10Hz，這裡就會休眠0.1s的樣子。
// %EndTag(RATE_SLEEP)%
    ++count;
  }


  return 0;
}
// %EndTag(FULLTEXT)%

一樣的，直接看程式碼，和程式碼中文註釋

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


/**
 * 下面是一個回撥函式。再定義接收器的時候會用到。
 * 看起來接收器實現的程式碼內部，會自動讓這個函式繫結一個
 * 訊息的指標。比如這裡，接受的訊息型別是std_msgs::String型別，和前面定義
 * 的釋出器釋出的訊息型別一樣。這裡抓到訊息，就用ROS_INFO命令，輸出到
 * 終端，讓我們看到。
*/

// %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;

  /**
   * 這個訂閱器的程式碼和之前的釋出其很類似，引數分別為節點名、快取大小。
   * 第三個引數和前面的回撥函式應該說過了。
   * 很好的解構函式保證了，物件被銷燬的時候，就不會再繼續訂閱了。
   */
// %Tag(SUBSCRIBER)%
  ros::Subscriber sub = n.subscribe("chatter", 1000, chatterCallback);
// %EndTag(SUBSCRIBER)%

  /**
   * spin()函式會進入一個迴圈，軟體實現中斷程式~？中斷級別之類的他怎麼實現呢- -#
   * 當然了，還是會接受ctrl+c之類的退出。
   */
// %Tag(SPIN)%
  ros::spin();
// %EndTag(SPIN)%

  return 0;
}
// %EndTag(FULLTEXT)%