ROS移动机器人——ROS基础知识与编程_ros机器人编程

此文章基于冰达机器人进行笔记整理，使用的环境为其配套环境，可结合之前的ROS，赵虚左老师的文章结合进行观看，后期也会进行整合

同时建议观看cn/ROS/Tutorials - ROS Wiki

官方教程

1. ROS安装

（1）配置ubuntu的软件和更新，允许安装不经认证的软件。

首先打开“软件和更新”对话框，具体可以在 Ubuntu 搜索按钮中搜索，确保勾选了"restricted"， "universe，" 和 "multiverse."

（2）设置安装源

来自国内中科大的安装源

sudo sh -c '. /etc/lsb-release && echo "deb http://mirrors.ustc.edu.cn/ros/ubuntu/ `lsb_release -cs` main" > /etc/apt/sources.list.d/ros-latest.list'

(3)设置key

sudo apt-key adv --keyserver 'hkp://keyserver.ubuntu.com:80' --recv-key C1CF6E31E6BADE8868B172B4F42ED6FBAB17C654

（4）安装

首先需要更新 apt(以前是 apt-get, 官方建议使用 apt 而非 apt-get),apt 是用于从互联网仓库搜索、安装、升级、卸载软件或操作系统的工具。

sudo apt update

然后，再安装所需类型的 ROS:ROS 多个类型:Desktop-Full、Desktop、ROS-Base。这里介绍较为常用的Desktop-Full(官方推荐)安装: ROS, rqt, rviz, robot-generic libraries, 2D/3D simulators, navigation and 2D/3D perception

sudo apt install ros-melodic-desktop-full

(5)配置环境变量

echo "source /opt/ros/melodic/setup.bash" >> ~/.bashrc
source ~/.bashrc

（6）安装依赖

依赖相关工具

sudo apt install python-rosdep python-rosinstall python-rosinstall-generator python-wstool build-essential

安装rosdep

sudo apt install python-rosdep

初始化rosdep

sudo rosdep init
rosdep update

（7） sudo rosdep init初始化失败的解决办法

 2. ROS通信结构

ROS的通信结构是在OS层之上，通过TCP/IP协议协议实现

节点NODE与主节点Master

 master：相当于管理中心，node也需要现在master进行注册，node的通信也是由master进行引线，才能进行通信，一个ros计算图里只能有一个master。

节点：一个可执行程序进程，通常一个node负责机器人的一个功能，也可以通过同一局域网作用与不同的机器人

（2）四种通信方式

 （3）话题与服务

(4)动作

· goal - 用于向服务器发送目标

· cancel - 用于向服务器发送取消请求

· status - 用于通知客户端系统中每个目标的2当前状态

· feedback - 用于周期反馈目标的辅助信息

· rssult - 用于向client发送任务的执行结果，这个topic指挥发送一次

 （5）参数服务器

 并非是一个node，运行在master中，节点储存参数的地方

常用的shell命令

一图流：

常用图形工具

1.

rqt_graph

 显示节点与节点之间的关系

2.

rqt_plot

 用于显示变量，查找关注的目标，同时改变坐标尺度，当我们移动乌龟时，图像也会跟着移动

3.查看摄像头/图像

//安装摄像头功能包
sudo apt install ros-melodic-uvc-camera

//运行
rosrun uvc_camera uvc_camera_node

这个话题如果使用echo的方式打印出来，图像是无法直接看出的，所以我们需要借助工具

rqt_image_view
 

同时选择我们的话题就可以查看

同时我们也可以使用roslaunch启动，roslaunch的机制如果我们没有启动roscore，他会自动帮我们启动，这个文件中为我们提供了launch，我们可以直接使用

roslaunch uvc_camera camera_node.launch

4. rviz

ros下，我们利用补齐就可以看到有许多工具，我们上面说明了一些重要的，同时还有一个rviz

他是一个强大的图像化显示工具，进行3d显示，2维也可以进行显示，我们之后再详细介绍

ROS坐标与TF变换

1.坐标定义法

2.rviz中显示坐标

 

当我们把两个小乌龟重合后，打开tf坐标

rosrun rqt_tf_tree rqt_tf_tree

可以有两个乌龟相对于中心坐标的位置

工作空间的创建与编译

 1.package.xml

该文件定义有关软件包的属性，例如软件包名称，版本号，作者，维护者以及对其他catkin软件包的依赖性。请注意，该概念类似于旧版 rosbuild 构建系统中使用的manifest.xml文件

​<?xml version="1.0"?>
<!-- 格式: 以前是 1，推荐使用格式 2 -->
<package format="2">
  <!-- 包名 -->
  <name>demo01_hello_vscode</name>
  <!-- 版本 -->
  <version>0.0.0</version>
  <!-- 描述信息 -->
  <description>The demo01_hello_vscode package</description>
 
  <!-- One maintainer tag required, multiple allowed, one person per tag -->
  <!-- Example:  -->
  <!-- <maintainer email="jane.doe@example.com">Jane Doe</maintainer> -->
  <!-- 维护人员 -->
  <maintainer email="xuzuo@todo.todo">xuzuo</maintainer>
 
 
  <!-- One license tag required, multiple allowed, one license per tag -->
  <!-- Commonly used license strings: -->
  <!--   BSD, MIT, Boost Software License, GPLv2, GPLv3, LGPLv2.1, LGPLv3 -->
  <!-- 许可证信息，ROS核心组件默认 BSD -->
  <license>TODO</license>
 
 
  <!-- Url tags are optional, but multiple are allowed, one per tag -->
  <!-- Optional attribute type can be: website, bugtracker, or repository -->
  <!-- Example: -->
  <!-- <url type="website">http://wiki.ros.org/demo01_hello_vscode</url> -->
 
 
  <!-- Author tags are optional, multiple are allowed, one per tag -->
  <!-- Authors do not have to be maintainers, but could be -->
  <!-- Example: -->
  <!-- <author email="jane.doe@example.com">Jane Doe</author> -->
 
 
  <!-- The *depend tags are used to specify dependencies -->
  <!-- Dependencies can be catkin packages or system dependencies -->
  <!-- Examples: -->
  <!-- Use depend as a shortcut for packages that are both build and exec dependencies -->
  <!--   <depend>roscpp</depend> -->
  <!--   Note that this is equivalent to the following: -->
  <!--   <build_depend>roscpp</build_depend> -->
  <!--   <exec_depend>roscpp</exec_depend> -->
  <!-- Use build_depend for packages you need at compile time: -->
  <!--   <build_depend>message_generation</build_depend> -->
  <!-- Use build_export_depend for packages you need in order to build against this package: -->
  <!--   <build_export_depend>message_generation</build_export_depend> -->
  <!-- Use buildtool_depend for build tool packages: -->
  <!--   <buildtool_depend>catkin</buildtool_depend> -->
  <!-- Use exec_depend for packages you need at runtime: -->
  <!--   <exec_depend>message_runtime</exec_depend> -->
  <!-- Use test_depend for packages you need only for testing: -->
  <!--   <test_depend>gtest</test_depend> -->
  <!-- Use doc_depend for packages you need only for building documentation: -->
  <!--   <doc_depend>doxygen</doc_depend> -->
  <!-- 依赖的构建工具，这是必须的 -->
  <buildtool_depend>catkin</buildtool_depend>
 
  <!-- 指定构建此软件包所需的软件包 -->
  <build_depend>roscpp</build_depend>
  <build_depend>rospy</build_depend>
  <build_depend>std_msgs</build_depend>
 
  <!-- 指定根据这个包构建库所需要的包 -->
  <build_export_depend>roscpp</build_export_depend>
  <build_export_depend>rospy</build_export_depend>
  <build_export_depend>std_msgs</build_export_depend>
 
  <!-- 运行该程序包中的代码所需的程序包 -->  
  <exec_depend>roscpp</exec_depend>
  <exec_depend>rospy</exec_depend>
  <exec_depend>std_msgs</exec_depend>
 
 
  <!-- The export tag contains other, unspecified, tags -->
  <export>
    <!-- Other tools can request additional information be placed here -->
 
  </export>
</package>

1.建立工作空间

mkdir catkin_ws

2.我们需要进入空间，创立src

cd catkin_ws/

3.我们的东西就要进入src目录下

mkdir src

4.将我们的包带进去

5.退出到目录

cd ..

 6.进行编译

catkin_make

7.我们还需要把工作空间加到环境变量里

vim .bashrc

ROS编程入门

工作空间的创建与编译

（1）ros文件内容介绍

WorkSpace --- 自定义的工作空间

    |--- build:编译空间，用于存放CMake和catkin的缓存信息、配置信息和其他中间文件。

    |--- devel:开发空间，用于存放编译后生成的目标文件，包括头文件、动态&静态链接库、可执行文件等。

    |--- src: 源码

        |-- package：功能包(ROS基本单元)包含多个节点、库与配置文件，包名所有字母小写，只能由字母、数字与下划线组成

            |-- CMakeLists.txt 配置编译规则，比如源文件、依赖项、目标文件

            |-- package.xml 包信息，比如:包名、版本、作者、依赖项...(以前版本是 manifest.xml)

            |-- scripts 存储python文件

            |-- src 存储C++源文件

            |-- include 头文件

            |-- msg 消息通信格式文件

            |-- srv 服务通信格式文件

            |-- action 动作格式文件

            |-- launch 可一次性运行多个节点 

            |-- config 配置信息

        |-- CMakeLists.txt: 编译的基本配置

1.package.xml

//该文件定义有关软件包的属性​
 
<?xml version="1.0"?>
<!-- 格式: 以前是 1，推荐使用格式 2 -->
<package format="2">
  <!-- 包名 -->
  <name>demo01_hello_vscode</name>
  <!-- 版本 -->
  <version>0.0.0</version>
  <!-- 描述信息 -->
  <description>The demo01_hello_vscode package</description>
 
  <!-- One maintainer tag required, multiple allowed, one person per tag -->
  <!-- Example:  -->
  <!-- <maintainer email="jane.doe@example.com">Jane Doe</maintainer> -->
  <!-- 维护人员 -->
  <maintainer email="xuzuo@todo.todo">xuzuo</maintainer>
 
 
  <!-- One license tag required, multiple allowed, one license per tag -->
  <!-- Commonly used license strings: -->
  <!--   BSD, MIT, Boost Software License, GPLv2, GPLv3, LGPLv2.1, LGPLv3 -->
  <!-- 许可证信息，ROS核心组件默认 BSD -->
  <license>TODO</license>
 
 
  <!-- Url tags are optional, but multiple are allowed, one per tag -->
  <!-- Optional attribute type can be: website, bugtracker, or repository -->
  <!-- Example: -->
  <!-- <url type="website">http://wiki.ros.org/demo01_hello_vscode</url> -->
 
 
  <!-- Author tags are optional, multiple are allowed, one per tag -->
  <!-- Authors do not have to be maintainers, but could be -->
  <!-- Example: -->
  <!-- <author email="jane.doe@example.com">Jane Doe</author> -->
 
 
  <!-- The *depend tags are used to specify dependencies -->
  <!-- Dependencies can be catkin packages or system dependencies -->
  <!-- Examples: -->
  <!-- Use depend as a shortcut for packages that are both build and exec dependencies -->
  <!--   <depend>roscpp</depend> -->
  <!--   Note that this is equivalent to the following: -->
  <!--   <build_depend>roscpp</build_depend> -->
  <!--   <exec_depend>roscpp</exec_depend> -->
  <!-- Use build_depend for packages you need at compile time: -->
  <!--   <build_depend>message_generation</build_depend> -->
  <!-- Use build_export_depend for packages you need in order to build against this package: -->
  <!--   <build_export_depend>message_generation</build_export_depend> -->
  <!-- Use buildtool_depend for build tool packages: -->
  <!--   <buildtool_depend>catkin</buildtool_depend> -->
  <!-- Use exec_depend for packages you need at runtime: -->
  <!--   <exec_depend>message_runtime</exec_depend> -->
  <!-- Use test_depend for packages you need only for testing: -->
  <!--   <test_depend>gtest</test_depend> -->
  <!-- Use doc_depend for packages you need only for building documentation: -->
  <!--   <doc_depend>doxygen</doc_depend> -->
  <!-- 依赖的构建工具，这是必须的 -->
  <buildtool_depend>catkin</buildtool_depend>
 
  <!-- 指定构建此软件包所需的软件包 -->
  <build_depend>roscpp</build_depend>
  <build_depend>rospy</build_depend>
  <build_depend>std_msgs</build_depend>
 
  <!-- 指定根据这个包构建库所需要的包 -->
  <build_export_depend>roscpp</build_export_depend>
  <build_export_depend>rospy</build_export_depend>
  <build_export_depend>std_msgs</build_export_depend>
 
  <!-- 运行该程序包中的代码所需的程序包 -->  
  <exec_depend>roscpp</exec_depend>
  <exec_depend>rospy</exec_depend>
  <exec_depend>std_msgs</exec_depend>
 
 
  <!-- The export tag contains other, unspecified, tags -->
  <export>
    <!-- Other tools can request additional information be placed here -->
 
  </export>
</package>

2.CMakelists.txt

//文件CMakeLists.txt是CMake构建系统的输入，用于构建软件包
 
​cmake_minimum_required(VERSION 3.0.2) #所需 cmake 版本
project(demo01_hello_vscode) #包名称，会被 ${PROJECT_NAME} 的方式调用
 
## Compile as C++11, supported in ROS Kinetic and newer
# add_compile_options(-std=c++11)
 
## Find catkin macros and libraries
## if COMPONENTS list like find_package(catkin REQUIRED COMPONENTS xyz)
## is used, also find other catkin packages
#设置构建所需要的软件包
find_package(catkin REQUIRED COMPONENTS
  roscpp
  rospy
  std_msgs
)
 
## System dependencies are found with CMake's conventions
#默认添加系统依赖
# find_package(Boost REQUIRED COMPONENTS system)
 
 
## Uncomment this if the package has a setup.py. This macro ensures
## modules and global scripts declared therein get installed
## See http://ros.org/doc/api/catkin/html/user_guide/setup_dot_py.html
# 启动 python 模块支持
# catkin_python_setup()
 
################################################
## Declare ROS messages, services and actions ##
## 声明 ROS 消息、服务、动作... ##
################################################
 
## To declare and build messages, services or actions from within this
## package, follow these steps:
## * Let MSG_DEP_SET be the set of packages whose message types you use in
##   your messages/services/actions (e.g. std_msgs, actionlib_msgs, ...).
## * In the file package.xml:
##   * add a build_depend tag for "message_generation"
##   * add a build_depend and a exec_depend tag for each package in MSG_DEP_SET
##   * If MSG_DEP_SET isn't empty the following dependency has been pulled in
##     but can be declared for certainty nonetheless:
##     * add a exec_depend tag for "message_runtime"
## * In this file (CMakeLists.txt):
##   * add "message_generation" and every package in MSG_DEP_SET to
##     find_package(catkin REQUIRED COMPONENTS ...)
##   * add "message_runtime" and every package in MSG_DEP_SET to
##     catkin_package(CATKIN_DEPENDS ...)
##   * uncomment the add_*_files sections below as needed
##     and list every .msg/.srv/.action file to be processed
##   * uncomment the generate_messages entry below
##   * add every package in MSG_DEP_SET to generate_messages(DEPENDENCIES ...)
## Generate messages in the 'msg' folder
# add_message_files(
#   FILES
#   Message1.msg
#   Message2.msg
# )
## Generate services in the 'srv' folder
# add_service_files(
#   FILES
#   Service1.srv
#   Service2.srv
# )
## Generate actions in the 'action' folder
# add_action_files(
#   FILES
#   Action1.action
#   Action2.action
# )
## Generate added messages and services with any dependencies listed here
# 生成消息、服务时的依赖包
# generate_messages(
#   DEPENDENCIES
#   std_msgs
# )
################################################
## Declare ROS dynamic reconfigure parameters ##
## 声明 ROS 动态参数配置 ##
################################################
## To declare and build dynamic reconfigure parameters within this
## package, follow these steps:
## * In the file package.xml:
##   * add a build_depend and a exec_depend tag for "dynamic_reconfigure"
## * In this file (CMakeLists.txt):
##   * add "dynamic_reconfigure" to
##     find_package(catkin REQUIRED COMPONENTS ...)
##   * uncomment the "generate_dynamic_reconfigure_options" section below
##     and list every .cfg file to be processed
## Generate dynamic reconfigure parameters in the 'cfg' folder
# generate_dynamic_reconfigure_options(
#   cfg/DynReconf1.cfg
#   cfg/DynReconf2.cfg
# )
###################################
## catkin specific configuration ##
## catkin 特定配置##
###################################
## The catkin_package macro generates cmake config files for your package
## Declare things to be passed to dependent projects
## INCLUDE_DIRS: uncomment this if your package contains header files
## LIBRARIES: libraries you create in this project that dependent projects also need
## CATKIN_DEPENDS: catkin_packages dependent projects also need
## DEPENDS: system dependencies of this project that dependent projects also need
# 运行时依赖
catkin_package(
#  INCLUDE_DIRS include
#  LIBRARIES demo01_hello_vscode
#  CATKIN_DEPENDS roscpp rospy std_msgs
#  DEPENDS system_lib
)
###########
## Build ##
###########
## Specify additional locations of header files
## Your package locations should be listed before other locations
# 添加头文件路径，当前程序包的头文件路径位于其他文件路径之前
include_directories(
# include
  ${catkin_INCLUDE_DIRS}
)
 
## Declare a C++ library
# 声明 C++ 库
# add_library(${PROJECT_NAME}
#   src/${PROJECT_NAME}/demo01_hello_vscode.cpp
# )
 
## Add cmake target dependencies of the library
## as an example, code may need to be generated before libraries
## either from message generation or dynamic reconfigure
# 添加库的 cmake 目标依赖
# add_dependencies(${PROJECT_NAME} ${${PROJECT_NAME}_EXPORTED_TARGETS} ${catkin_EXPORTED_TARGETS})
 
## Declare a C++ executable
## With catkin_make all packages are built within a single CMake context
## The recommended prefix ensures that target names across packages don't collide
# 声明 C++ 可执行文件
add_executable(Hello_VSCode src/Hello_VSCode.cpp)
 
## Rename C++ executable without prefix
## The above recommended prefix causes long target names, the following renames the
## target back to the shorter version for ease of user use
## e.g. "rosrun someones_pkg node" instead of "rosrun someones_pkg someones_pkg_node"
#重命名c++可执行文件
# set_target_properties(${PROJECT_NAME}_node PROPERTIES OUTPUT_NAME node PREFIX "")
 
## Add cmake target dependencies of the executable
## same as for the library above
#添加可执行文件的 cmake 目标依赖
add_dependencies(Hello_VSCode ${${PROJECT_NAME}_EXPORTED_TARGETS} ${catkin_EXPORTED_TARGETS})
 
## Specify libraries to link a library or executable target against
#指定库、可执行文件的链接库
target_link_libraries(Hello_VSCode
  ${catkin_LIBRARIES}
)
 
#############
## Install ##
## 安装 ##
#############
 
# all install targets should use catkin DESTINATION variables
# See http://ros.org/doc/api/catkin/html/adv_user_guide/variables.html
 
## Mark executable scripts (Python etc.) for installation
## in contrast to setup.py, you can choose the destination
#设置用于安装的可执行脚本
catkin_install_python(PROGRAMS
  scripts/Hi.py
  DESTINATION ${CATKIN_PACKAGE_BIN_DESTINATION}
)
## Mark executables for installation
## See http://docs.ros.org/melodic/api/catkin/html/howto/format1/building_executables.html
# install(TARGETS ${PROJECT_NAME}_node
#   RUNTIME DESTINATION ${CATKIN_PACKAGE_BIN_DESTINATION}
# )
 
## Mark libraries for installation
## See http://docs.ros.org/melodic/api/catkin/html/howto/format1/building_libraries.html
# install(TARGETS ${PROJECT_NAME}
#   ARCHIVE DESTINATION ${CATKIN_PACKAGE_LIB_DESTINATION}
#   LIBRARY DESTINATION ${CATKIN_PACKAGE_LIB_DESTINATION}
#   RUNTIME DESTINATION ${CATKIN_GLOBAL_BIN_DESTINATION}
# )
 
## Mark cpp header files for installation
# install(DIRECTORY include/${PROJECT_NAME}/
#   DESTINATION ${CATKIN_PACKAGE_INCLUDE_DESTINATION}
#   FILES_MATCHING PATTERN "*.h"
#   PATTERN ".svn" EXCLUDE
# )
 
## Mark other files for installation (e.g. launch and bag files, etc.)
# install(FILES
#   # myfile1
#   # myfile2
#   DESTINATION ${CATKIN_PACKAGE_SHARE_DESTINATION}
# )
 
#############
## Testing ##
#############
 
## Add gtest based cpp test target and link libraries
# catkin_add_gtest(${PROJECT_NAME}-test test/test_demo01_hello_vscode.cpp)
# if(TARGET ${PROJECT_NAME}-test)
#   target_link_libraries(${PROJECT_NAME}-test ${PROJECT_NAME})
# endif()
 
## Add folders to be run by python nosetests
# catkin_add_nosetests(test)

（2）话题通信基本操作

在模型实现中，ROS master 不需要实现，而连接的建立也已经被封装了，需要关注的关键点有三个:

1. 发布方
2. 接收方
3. 数据(此处为普通文本)

所以我们需要实现的流程为：

1. 编写发布方实现；
2. 编写订阅方实现；
3. 编辑配置文件；
4. 编译并执行。

需求：实现通信，一方接受，一方发送

消息发布方： helloworld + 计数

      

// 1.包含头文件 
#include "ros/ros.h"
#include "std_msgs/String.h" //普通文本类型的消息
#include <sstream>
 
int main(int argc, char  *argv[])
{   
    //设置编码
    setlocale(LC_ALL,"");
 
    //2.初始化 ROS 节点:命名(唯一)
    // 参数1和参数2 后期为节点传值会使用
    // 参数3 是节点名称，是一个标识符，需要保证运行后，在 ROS 网络拓扑中唯一
    ros::init(argc,argv,"talker");
    //3.实例化 ROS 句柄
    ros::NodeHandle nh;//该类封装了 ROS 中的一些常用功能
 
    //4.实例化 发布者 对象
    //泛型: 发布的消息类型
    //参数1: 要发布到的话题
    //参数2: 队列中最大保存的消息数，超出此阀值时，先进的先销毁(时间早的先销毁)
    ros::Publisher pub = nh.advertise<std_msgs::String>("chatter",10);
 
    //5.组织被发布的数据，并编写逻辑发布数据
    //数据(动态组织)
    std_msgs::String msg;
    // msg.data = "你好啊！！！";
    std::string msg_front = "Hello 你好！"; //消息前缀
    int count = 0; //消息计数器
 
    //逻辑(一秒10次)
    ros::Rate r(1);
 
    //节点不死
    while (ros::ok())
    {
        //使用 stringstream 拼接字符串与编号
        std::stringstream ss;
        ss << msg_front << count;
        msg.data = ss.str();
        //发布消息
        pub.publish(msg);
        //加入调试，打印发送的消息
        ROS_INFO("发送的消息:%s",msg.data.c_str());
 
        //根据前面制定的发送贫频率自动休眠 休眠时间 = 1/频率；
        r.sleep();
        count++;//循环结束前，让 count 自增
        //暂无应用
        ros::spinOnce();
    }
 
 
    return 0;
}

编辑法2（冰达）

1. 建立文件 talker.cpp 用于通信的发布者

2. 包含头文件

// ros头文件
#include "ros/ros.h"
//普通文本类型的消息
#include "std_msgs/String.h" 

3. 写标准main函数、（m）

int main(int argc,char **argv)
{
  //初始化ros,三个参数，最后一个为节点名称
  ros::init(argc,argv,"talker");
  //不能在一个ros中运行两个节点，所以要创建句点
  ros:NodeHandle n;
   // 创建发布器,最后为发布类型string，发布的消息名为chatter,1000个，储存我们的消息
  ros:Publisher chatter_pub = n.advertise<std_msgs::String>("chatter",1000);
  
  //创建一个循环，这里用10hz
  ros:Rate loop_rate(10);
  //记数，查看一共有多少个话题
  int count = 0;
 
  //写一个死循环，让他发送消息
  while(ros::ok()) // 当收到ctrl + c就会停止
{
   std_msgs::String msg; //名字为msg
   std:stringstream ss;  // 命名消息
   ss<<"hello world"<<count;  //消息格式（内容）
   msg.data = ss.str();  //将ss赋值给数据data
   ROS_INFO("%s",msg.data.c_str());
   chatter_pub.publish(msg);
   ros::spinOnce();
   loop_rate.sleep();
  
   count++:
}
  
 
  
   
 
}

接下来我们来看看订阅者

#include "ros/ros.h"
#include "std_msgs/String"
 
 
void chatterCallback(const std_msgs::StringConstPtr&msg)
{
   ROS_INFO("i heard:[%s] ",msg.data.c_str()); //以字符串形式
 
}
 
int main(int argc,char **argv)
{
    ros::init(argc,argv, "Listener");
    ros::NodeHandle n;
    ros::Subcriber sub=n.subcribe("chatter",1000,chatterCallback);
    ros::spin(); //循环
    
    return 0;
}