准备工作
创建工作空间
<code class="prism language-bash has-numbering">$ <span class="token function">mkdir</span> -p ～/catkin_ws/src $ <span class="token function">cd</span> ～/catkin_ws/src $ catkin_init_workspace</code>
进入代码空间，使用catkin_create_pkg命令创建功能包：
<code class="prism language-bash has-numbering">$ <span class="token function">cd</span> ～/catkin_ws/src $ catkin_create_pkg learning_communication std_msgs rospy roscpp</code>
然后回到工作空间的根目录下进行编译，并且设置环境变量：
<code class="prism language-bash has-numbering">$ <span class="token function">cd</span> ～/catkin_ws $ catkin_make $ <span class="token function">source</span> ～/catkin_ws/devel/setup.bash</code>
工作空间和功能包的创建这里就不过多重复讲了
创建Publisher
Publisher的主要作用是针对指定话题发布特定数据类型的消息。我们尝试使用代码实现一个节点，节点中创建一个Publisher并发布字符串“Hello World”。 在功能包（暂命名为learning——communication）的src文件夹里建立一个talker.cpp文件，内容为： （此处注释比较详细，大家可以直接下载我整理好的功能包去运行：）
<code class="prism language-cpp has-numbering"><span class="token macro property">#<span class="token directive keyword">include</span> <span class="token string"><sstream></span></span>
<span class="token macro property">#<span class="token directive keyword">include</span> <span class="token string">"ros/ros.h"</span></span>
<span class="token macro property">#<span class="token directive keyword">include</span> <span class="token string">"std_msgs/String.h"</span></span>
<span class="token comment">//为了避免包含繁杂的ROS功能包头文件，ros/ros.h已经帮我们包含了大部分ROS中通用的头文件。节点会发布String类型的消息，所以需要先包含该消息类型的头文件String.h。该头文件根据String.msg的消息结构定义自动生成，我们也可以自定义消息结构，并生成所需要的头文件。</span>
<span class="token keyword">int</span> <span class="token function">main</span><span class="token punctuation">(</span><span class="token keyword">int</span> argc<span class="token punctuation">,</span> <span class="token keyword">char</span> <span class="token operator">*</span><span class="token operator">*</span>argv<span class="token punctuation">)</span>
<span class="token punctuation">{</span>
<span class="token comment">// ROS节点初始化：初始化ROS节点。该初始化的init函数包含三个参数，前两个参数是命令行或launch文件输入的参数，可以用来完成命名重映射等功能；第三个参数定义了Publisher节点的名称，而且该名称在运行的ROS中必须是独一无二的，不允许同时存在相同名称的两个节点。</span>
ros<span class="token operator">::</span><span class="token function">init</span><span class="token punctuation">(</span>argc<span class="token punctuation">,</span> argv<span class="token punctuation">,</span> <span class="token string">"talker"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">// 创建节点句柄，，方便对节点资源的使用和管理。</span>
ros<span class="token operator">::</span>NodeHandle n<span class="token punctuation">;</span>
<span class="token comment">// 创建一个Publisher，发布名为chatter的topic，消息类型为std_msgs::String，第二个参数表示消息发布队列的大小，当发布消息的实际速度较慢时，Publisher会将消息存储在一定空间的队列中；如果消息数量超过队列大小时，ROS会自动删除队列中最早入队的消息。</span>
ros<span class="token operator">::</span>Publisher chatter_pub <span class="token operator">=</span> n<span class="token punctuation">.</span>advertise<span class="token operator"><</span>std_msgs<span class="token operator">::</span>String<span class="token operator">></span><span class="token punctuation">(</span><span class="token string">"chatter"</span><span class="token punctuation">,</span> <span class="token number">1000</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">// 设置循环的频率，单位是Hz，这里设置的是10 Hz。当调用Rate：sleep（）时，ROS节点会根据此处设置的频率休眠相应的时间，以保证循环维持一致的时间周期。</span>
ros<span class="token operator">::</span>Rate <span class="token function">loop_rate</span><span class="token punctuation">(</span><span class="token number">10</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">int</span> count <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span>
<span class="token keyword">while</span> <span class="token punctuation">(</span>ros<span class="token operator">::</span><span class="token function">ok</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span>
<span class="token punctuation">{</span>
<span class="token comment">//进入节点的主循环，在节点未发生异常的情况下将一直在循环中运行，一旦发生异常，ros：ok（）就会返回false，跳出循环。</span>
<span class="token comment">// 初始化std_msgs::String类型的消息，这里我们使用了最为简单的String消息类型，该消息类型只有一个成员，即data，用来存储字符串数据。</span>
std_msgs<span class="token operator">::</span>String msg<span class="token punctuation">;</span>
std<span class="token operator">::</span>stringstream ss<span class="token punctuation">;</span>
ss <span class="token operator"><<</span> <span class="token string">"hello world "</span> <span class="token operator"><<</span> count<span class="token punctuation">;</span>
msg<span class="token punctuation">.</span>data <span class="token operator">=</span> ss<span class="token punctuation">.</span><span class="token function">str</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">// 发布封装完毕的消息msg。消息发布后，Master会查找订阅该话题的节点，并且帮助两个节点建立连接，完成消息的传输。</span>
<span class="token function">ROS_INFO</span><span class="token punctuation">(</span><span class="token string">"%s"</span><span class="token punctuation">,</span> msg<span class="token punctuation">.</span>data<span class="token punctuation">.</span><span class="token function">c_str</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
chatter_pub<span class="token punctuation">.</span><span class="token function">publish</span><span class="token punctuation">(</span>msg<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">// 循环等待回调函数</span>
ros<span class="token operator">::</span><span class="token function">spinOnce</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">// 按照循环频率延时，现在Publisher一个周期的工作已经完成，可以让节点休息一段时间，调用休眠函数，节点进入休眠状态。当然，节点不可能一直休眠下去，别忘了之前设置了10Hz的休眠时间，节点休眠100ms后又会开始下一个周期的循环工作。</span>
loop_rate<span class="token punctuation">.</span><span class="token function">sleep</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token operator">++</span>count<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword">return</span> <span class="token number">0</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span></code>
实现Publisher的流程可总结为： 初始化ROS节点→在ROS Master注册节点信息→按照一定的频率发布消息
创建Subscriber
创建一个Subscriber以订阅Publisher节点发布的“Hello World”字符串 在功能包的src文件夹里建立一个listener.cpp文件，内容为： （和talker.cpp中重复的代码部分不再详细注释）
<code class="prism language-cpp has-numbering"><span class="token macro property">#<span class="token directive keyword">include</span> <span class="token string">"ros/ros.h"</span></span>
<span class="token macro property">#<span class="token directive keyword">include</span> <span class="token string">"std_msgs/String.h"</span></span>
<span class="token comment">// 接收到订阅的消息后，会进入消息回调函数</span>
<span class="token comment">//回调函数是订阅节点接收消息的基础机制，当有消息到达时会自动以消息指针作为参数，再调用回调函数，完成对消息内容的处理。如上是一个简单的回调函数，用来接收Publisher发布的String消息，并将消息数据打印出来。</span>
<span class="token keyword">void</span> <span class="token function">chatterCallback</span><span class="token punctuation">(</span><span class="token keyword">const</span> std_msgs<span class="token operator">::</span>String<span class="token operator">::</span>ConstPtr<span class="token operator">&</span> msg<span class="token punctuation">)</span>
<span class="token punctuation">{</span>
<span class="token comment">// 将接收到的消息打印出来</span>
<span class="token function">ROS_INFO</span><span class="token punctuation">(</span><span class="token string">"I heard: [%s]"</span><span class="token punctuation">,</span> msg<span class="token operator">-</span><span class="token operator">></span>data<span class="token punctuation">.</span><span class="token function">c_str</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword">int</span> <span class="token function">main</span><span class="token punctuation">(</span><span class="token keyword">int</span> argc<span class="token punctuation">,</span> <span class="token keyword">char</span> <span class="token operator">*</span><span class="token operator">*</span>argv<span class="token punctuation">)</span>
<span class="token punctuation">{</span>
<span class="token comment">// 初始化ROS节点</span>
ros<span class="token operator">::</span><span class="token function">init</span><span class="token punctuation">(</span>argc<span class="token punctuation">,</span> argv<span class="token punctuation">,</span> <span class="token string">"listener"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">// 创建节点句柄</span>
ros<span class="token operator">::</span>NodeHandle n<span class="token punctuation">;</span>
<span class="token comment">// 创建一个Subscriber，订阅名为chatter的话题，注册回调函数chatterCallback</span>
<span class="token comment">//订阅节点首先需要声明自己订阅的消息话题，该信息会在ROS Master中注册。Master会关注系统中是否存在发布该话题的节点，如果存在则会帮助两个节点建立连接，完成数据传输。</span>
<span class="token comment">//NodeHandle：subscribe（），这里为n.subscribe,用来创建一个Subscriber。第一个参数即为消息话题；第二个参数是接收消息队列的大小，和发布节点的队列相似，当消息入队数量超过设置的队列大小时，会自动舍弃时间戳最早的消息；第三个参数是接收到话题消息后的回调函数。</span>
ros<span class="token operator">::</span>Subscriber sub <span class="token operator">=</span> n<span class="token punctuation">.</span><span class="token function">subscribe</span><span class="token punctuation">(</span><span class="token string">"chatter"</span><span class="token punctuation">,</span> <span class="token number">1000</span><span class="token punctuation">,</span> chatterCallback<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">// 循环等待回调函数，ros：spin（）在ros：ok（）返回false时退出。</span>
ros<span class="token operator">::</span><span class="token function">spin</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">return</span> <span class="token number">0</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span></code>
实现Subscriber的流程可总结为： 初始化ROS节点→订阅需要的话题→循环等待话题消息，接收到消息后进入回调函数→回调函数中完成消息处理。 编译功能包 节点的代码已经完成，C++是一种编译语言，在运行之前需要将代码编译成可执行文件，如果使用Python等解析语言编写代码，则不需要进行编译，可以省去此步骤。 ROS中的编译器使用的是CMake，编译规则通过功能包中的CMakeLists.txt文件设置，使用catkin命令创建的功能包中会自动生成该文件，已经配置多数编译选项，并且包含详细的注释，我们几乎不用查看相关的说明手册，稍作修改就可以编译自己的代码。 打开功能包中的CMakeLists.txt文件，找到以下配置项，去掉注释并稍作修改：
<code class="prism language-cpp has-numbering"><span class="token function">include_directories</span><span class="token punctuation">(</span>include $<span class="token punctuation">{</span>catkin_INCLUDE_DIRS<span class="token punctuation">}</span><span class="token punctuation">)</span>
<span class="token function">add_executable</span><span class="token punctuation">(</span>talker src<span class="token operator">/</span>talker<span class="token punctuation">.</span>cpp<span class="token punctuation">)</span>
<span class="token function">target_link_libraries</span><span class="token punctuation">(</span>talker $<span class="token punctuation">{</span>catkin_LIBRARIES<span class="token punctuation">}</span><span class="token punctuation">)</span>
<span class="token function">add_dependencies</span><span class="token punctuation">(</span>talker $<span class="token punctuation">{</span>PROJECT_NAME<span class="token punctuation">}</span>_generate_messages_cpp<span class="token punctuation">)</span>
<span class="token function">add_executable</span><span class="token punctuation">(</span>listener src<span class="token operator">/</span>listener<span class="token punctuation">.</span>cpp<span class="token punctuation">)</span>
<span class="token function">target_link_libraries</span><span class="token punctuation">(</span>listener $<span class="token punctuation">{</span>catkin_LIBRARIES<span class="token punctuation">}</span><span class="token punctuation">)</span>
<span class="token function">add_dependencies</span><span class="token punctuation">(</span>talker $<span class="token punctuation">{</span>PROJECT_NAME<span class="token punctuation">}</span>_generate_messages_cpp<span class="token punctuation">)</span></code>
对于这个功能包，主要用到了以下四种编译配置项： （1）include_directories 用于设置头文件的相对路径。全局路径默认是功能包的所在目录，比如功能包的头文件一般会放到功能包根目录下的include文件夹中，所以此处需要添加该文件夹。此外，该配置项还包含ROS catkin编译器默认包含的其他头文件路径，比如ROS默认安装路径、Linux系统路径等。 （2）add_executable 用于设置需要编译的代码和生成的可执行文件。第一个参数为期望生成的可执行文件的名称，后边的参数为参与编译的源码文件（cpp），如果需要多个代码文件，则可在后面依次列出，中间使用空格进行分隔。 （3）target_link_libraries 用于设置链接库。很多功能需要使用系统或者第三方的库函数，通过该选项可以配置执行文件链接的库文件，其第一个参数与add_executable相同，是可执行文件的名称，后面依次列出需要链接的库。此处编译的Publisher和Subscriber没有使用其他库，添加默认链接库即可。 （4）add_dependencies 用于设置依赖。在很多应用中，我们需要定义语言无关的消息类型，消息类型会在编译过程中产生相应语言的代码，如果编译的可执行文件依赖这些动态生成的代码，则需要使用add_dependencies添加${PROJECT_NAME}_generate_messages_cpp配置，即该功能包动态产生的消息代码。该编译规则也可以添加其他需要依赖的功能包。 以上编译内容会帮助系统生成两个可执行文件：talker和listener，放置在工作空间的～/catkin_ws/devel/lib/路径下。 CMakeLists.txt修改完成后，在工作空间的根路径下开始编译：
<code class="prism language-bash has-numbering">$ <span class="token function">cd</span> ～/catkin_ws $ catkin_make</code>
运行Publisher与Subscriber
首先要设置环境变量：
<code class="prism language-bash has-numbering">$ <span class="token function">cd</span> ～/catkin_ws $ <span class="token function">source</span> ./devel/setup.bash</code>
也可以将环境变量的配置脚本添加到终端的配置文件中：
<code class="prism language-bash has-numbering">$ <span class="token keyword">echo</span> <span class="token string">"source ～/catkin_ws/devel/setup.bash"</span> <span class="token operator">>></span> ～/.bashrc $ <span class="token function">source</span> ～/.bashrc</code>
设置好之后就可以进入启动步骤了： 1.请出ROS master
<code class="prism language-bash has-numbering">$ roscore </code>
2．启动Publisher
<code class="prism language-bash has-numbering">$ rosrun learning_communication talker </code>
3.启动Subscriber
<code class="prism language-bash has-numbering">$ rosrun learning_communication listener </code>
/
//可以看到，消息已经实现同步的发布和订阅了 若关闭talker的话，会看待listener马上停止
下面说一下ROS下 上位机与Arduino单片机通讯
ROS下 上位机与Arduino单片机通讯
对于Arduino IDE的配置安装和串口通讯，请点这里 Publisher示例 主要就是如何通过rosserial创建publisher 例子来自Arduino IDE，File->Example->ros_lib下的HelloWord，下面给大家简单注释一下
<code class="prism language-cpp has-numbering"><span class="token macro property">#<span class="token directive keyword">include</span> <span class="token string"><ros.h></span></span>
<span class="token macro property">#<span class="token directive keyword">include</span> <span class="token string"><std_msgs/String.h></span> </span>
<span class="token comment">//创建节点句柄</span>
ros<span class="token operator">::</span>NodeHandle nh<span class="token punctuation">;</span>
<span class="token comment">// 声明一个消息对象str_msg。其参数为data内容为消息内容。</span>
std_msgs<span class="token operator">::</span>String str_msg<span class="token punctuation">;</span>
<span class="token comment">// 发布一个话题，名字叫做chatter，消息内容</span>
ros<span class="token operator">::</span>Publisher <span class="token function">chatter</span><span class="token punctuation">(</span><span class="token string">"chatter"</span><span class="token punctuation">,</span> <span class="token operator">&</span>str_msg<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">char</span> hello<span class="token punctuation">[</span><span class="token number">13</span><span class="token punctuation">]</span> <span class="token operator">=</span> <span class="token string">"hello world!"</span><span class="token punctuation">;</span>
<span class="token keyword">void</span> <span class="token function">setup</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
<span class="token punctuation">{</span>
nh<span class="token punctuation">.</span><span class="token function">initNode</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
nh<span class="token punctuation">.</span><span class="token function">advertise</span><span class="token punctuation">(</span>chatter<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword">void</span> <span class="token function">loop</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
<span class="token punctuation">{</span>
str_msg<span class="token punctuation">.</span>data <span class="token operator">=</span> hello<span class="token punctuation">;</span>
chatter<span class="token punctuation">.</span><span class="token function">publish</span><span class="token punctuation">(</span> <span class="token operator">&</span>str_msg <span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//发布一个消息 话题.publish(&消息)</span>
nh<span class="token punctuation">.</span><span class="token function">spinOnce</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token function">delay</span><span class="token punctuation">(</span><span class="token number">1000</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span></code>
接下来打开终端分别运行 1.把ros master请出来
<code class="prism language-bash has-numbering">roscore </code>
2.新终端运行，/dev/ttyUSB0为Arduino设备
<code class="prism language-bash has-numbering">rosrun rosserial_python serial_node.py /dev/ttyUSB0 </code>
3.显示主题chatter，获取Arduino板反馈的信息
<code class="prism language-bash has-numbering">rostopic <span class="token keyword">echo</span> chatter </code>
Subscriber示例 主要就是如何通过rosserial创建subscriber，点亮Arduino上的LED灯 例子来自Arduino IDE，File->Example->ros_lib下的blink，下面给大家简单注释一下
<code class="prism language-cpp has-numbering"><span class="token comment">/*
* rosserial Subscriber Example
* Blinks an LED on callback
*/</span>
<span class="token comment">//必需包含的ros头文件和消息头文件</span>
<span class="token macro property">#<span class="token directive keyword">include</span> <span class="token string"><ros.h></span></span>
<span class="token macro property">#<span class="token directive keyword">include</span> <span class="token string"><std_msgs/Empty.h></span></span>
ros<span class="token operator">::</span>NodeHandle nh<span class="token punctuation">;</span>
<span class="token comment">//创建回调函数messageCb，必需传递常量消息引用值作为参数，这里函数是messageCb。</span>
<span class="token comment">//消息类型是std_msgs::Empty，消息名称是toggle_msg</span>
<span class="token comment">//在函数内，我们可以引用toggle_msg，但它是空的，就不必要了。</span>
<span class="token comment">//Arduino每次收到信息就会点亮灯。</span>
<span class="token keyword">void</span> <span class="token function">messageCb</span><span class="token punctuation">(</span> <span class="token keyword">const</span> std_msgs<span class="token operator">::</span>Empty<span class="token operator">&</span> toggle_msg<span class="token punctuation">)</span><span class="token punctuation">{</span>
<span class="token function">digitalWrite</span><span class="token punctuation">(</span><span class="token number">13</span><span class="token punctuation">,</span> HIGH<span class="token operator">-</span><span class="token function">digitalRead</span><span class="token punctuation">(</span><span class="token number">13</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// blink the led</span>
<span class="token punctuation">}</span>
<span class="token comment">//这里实例化订阅，有两个参数，主题名toggle_led和回调函数名，标明主题的消息类型std_msgs::Empty</span>
ros<span class="token operator">::</span>Subscriber<span class="token operator"><</span>std_msgs<span class="token operator">::</span>Empty<span class="token operator">></span> <span class="token function">sub</span><span class="token punctuation">(</span><span class="token string">"toggle_led"</span><span class="token punctuation">,</span> <span class="token operator">&</span>messageCb <span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">void</span> <span class="token function">setup</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
<span class="token punctuation">{</span>
<span class="token comment">//初始化ROS节点处理，并宣告所有的发布或订阅</span>
<span class="token function">pinMode</span><span class="token punctuation">(</span><span class="token number">13</span><span class="token punctuation">,</span> OUTPUT<span class="token punctuation">)</span><span class="token punctuation">;</span>
nh<span class="token punctuation">.</span><span class="token function">initNode</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
nh<span class="token punctuation">.</span><span class="token function">subscribe</span><span class="token punctuation">(</span>sub<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword">void</span> <span class="token function">loop</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
<span class="token punctuation">{</span>
<span class="token comment">//在Arduino的loop函数，调用nh.spinOnce()，这样所有的ROS回调函数就会被处理。</span>
nh<span class="token punctuation">.</span><span class="token function">spinOnce</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token function">delay</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span></code>
1.请出master
<code class="prism language-bash has-numbering">$ roscore </code>
2.新终端运行，/dev/ttyUSB0为Arduino设备
<code class="prism language-bash has-numbering">$ rosrun rosserial_python serial_node.py /dev/ttyUSB0 </code>
<code class="prism language-bash has-numbering"></code>
3.发布主题，点亮Arduino板上的LED灯
<code class="prism language-bash has-numbering">$ rostopic pub toggle_led std_msgs/Empty --once </code>
开心洋葱 , 版权所有丨如未注明 , 均为原创丨未经授权请勿修改 , 转载请注明ROS中话题的订阅与发布+ROS环境下上位机与Arduino单片机通讯！
