创建ROS程序包及节点

一、创建功能包

打开终端，输入下面指令。

cd catkin_ws/src 
catkin_create_pkg learning_msg roscpp rospy std_msgs

在catkin_ws命名空间的src文件夹下，用
catkin_create_pkg指令创建功能包，格式如下：
catkin_create_pkg 功能包名称 依赖项1 依赖项2 …

二、创建节点

进入learning_msg 功能包的src文件夹内，创建发布节点。

roscd learning_msg 
cd src 
gedit msg_publisher.cpp

#include "ros/ros.h" //导入ROS系统包含核心公共头文件 
#include "std_msgs/String.h" //导入std_msgs/String消息头文件，这个是由std_m sgs包的string.msg文件自动生成。
#include <sstream> 
int main(int argc, char **argv) 
{ 
    ros::init(argc, argv, "msg_publisher"); //初始化ROS，指定节点名称为“msg_publisher”，节点名称要保持唯一性。名称定义参考 
    ros::NodeHandle n; //实例化节点 
    ros::Publisher chatter_pub = n.advertise<std_msgs::String>("chatter", 1000); //发布一个消息类型为std_msgs/String，命名为chatter的话题。 
    //定义消息队列大小为1000，即超过1000条消息之后，旧的消息就会丢弃。
    ros::Rate loop_rate(10); //指定发布消息的频率，这里指10Hz，也即每秒10次 
    //通过 Rate::sleep()来处理睡眠的时间来控制对应的发布频率。 
    int count = 0; 
    while (ros::ok()) 
    { 
        /* 
        默认roscpp会植入一个SIGINT处理机制，当按下Ctrl‐C，就会让ros::ok()返回false, 那循环就会结束。 
        ros::ok() 返回false的几种情况： 
        SIGINT收到(Ctrl‐C)信号 
        另一个同名节点启动，会先中止之前的同名节点 
        ros::shutdown()被调用
        所有的ros::NodeHandles被销毁 
        */ 
        std_msgs::String msg; 
        std::stringstream ss; 
        ss << "hello world " << count; 
        msg.data = ss.str(); 
        //实例化消息msg, 定义字符串流“hello world”并赋值给ss, 最后转成为字符串赋值给 msg.data 
        ROS_INFO("%s", msg.data.c_str()); //输出调试信息 
        chatter_pub.publish(msg); //发布msg 
        ros::spinOnce(); 
        //不是必需的，但是保持增加这个调用，是好习惯 
        //如果程序里也有订阅话题，就必需，否则回调函数不能起作用 
        loop_rate.sleep(); 
        //根据之前ros::Rate loop_rate(10)的定义来控制发布话题的频率。定义10即为每秒1 0次
        ++count; 
    } 
    return 0; 
}

发布节点的功能就是发布hello world并计数。发布节点的名称 是msg_publisher，发布 的话题为chatter，发布的内容是hello world + 计数。只要Master节点管理器不死，就会移植发布。
有了发布节点，接下来需要做一个订阅节点来接收这些数据。

roscd learning_msg 
cd src 
gedit msg_listener.cpp

#include "ros/ros.h" //导入ROS系统包含核心公共头文件 
#include "std_msgs/String.h" //导入std_msgs/String消息头文件，这个是由std_m sgs包的string.msg文件自动生成。 
/* 
定义回调函数chatterCallback，当收到chatter话题的消息就会调用这个函数。
消息通过boost shared_ptr（共享指针）来传递。 
但收到消息，通过ROS_INFO函数显示到终端 
*/ 
void chatterCallback(const std_msgs::String::ConstPtr& msg) 
{ 
    ROS_INFO("I heard: [%s]", msg->data.c_str()); 
} 
int main(int argc, char **argv) 
{ 
    ros::init(argc, argv, "msg_listener"); //初始化ROS，指定节点名称为“msg_listener” 
    ros::NodeHandle n; //实例化节点 
    ros::Subscriber sub = n.subscribe("chatter", 1000, chatterCallback); 
    /* 
    定义订阅节点，名称为chatter，指定回调函数chatterCallback 
    但收到消息，则调用函数chatterCallback来处理。 
    参数1000，定义队列大小，如果处理不够快，超过1000，则丢弃旧的消息 
    */ 

     ros::spin(); //调用此函数才真正开始进入循环处理，直到 ros::ok()返回false才停 止。
     return 0; 
 }

订阅节点使用类似中断的方式，也就是信号回调来实现，只要检测到有chatter消息就打印出来。

三、配置package.xml

<?xml version="1.0"?>
<package format="2">
  <name>learning_msg</name>
  <version>0.0.0</version>
  <description>The learning_msg package</description>

  <!-- One maintainer tag required, multiple allowed, one person per tag -->
  <!-- Example:  -->
  <!-- <maintainer email="jane.doe@example.com">Jane Doe</maintainer> -->
  <maintainer email="wanghq@todo.todo">wanghq</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 -->
  <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/learning_msg</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> -->
  <buildtool_depend>catkin</buildtool_depend>
  <build_depend>roscpp</build_depend>
  <build_depend>rospy</build_depend>
  <build_depend>std_msgs</build_depend>
  <build_depend>message_generation</build_depend> 
  <build_export_depend>roscpp</build_export_depend>
  <build_export_depend>rospy</build_export_depend>
  <build_export_depend>std_msgs</build_export_depend>
  <exec_depend>roscpp</exec_depend>
  <exec_depend>rospy</exec_depend>
  <exec_depend>std_msgs</exec_depend>
  <exec_depend>message_runtime</exec_depend> 


  <!-- The export tag contains other, unspecified, tags -->
  <export>
    <!-- Other tools can request additional information be placed here -->

在包依赖中增加消息生成项，分别为：

<build_depend>message_generation</build_depend> 

和

<exec_depend>message_runtime</exec_depend>

前者用于编译过程，后者用于执行过程。

四、修改CMakeList.txt

cmake_minimum_required(VERSION 3.0.2)
project(learning_msg)

## 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
find_package(catkin REQUIRED COMPONENTS
  roscpp
  rospy
  std_msgs
  message_generation
)

## System dependencies are found with CMake's conventions
# 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
# catkin_python_setup()

################################################
## Declare ROS messages, services and actions ##
################################################

## 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
 generate_messages(
   DEPENDENCIES
   std_msgs
 )

################################################
## Declare ROS dynamic reconfigure parameters ##
################################################

## 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 ##
###################################
## 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
catkin_package(
#  INCLUDE_DIRS include
#  LIBRARIES learning_msg
 CATKIN_DEPENDS roscpp rospy std_msgs message_runtime
#  DEPENDS system_lib
)

###########
## Build ##
###########

## Specify additional locations of header files
## Your package locations should be listed before other locations
include_directories(
 include
  ${catkin_INCLUDE_DIRS}
)

## Declare a C++ library
# add_library(${PROJECT_NAME}
#   src/${PROJECT_NAME}/learning_msg.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
# 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
# add_executable(${PROJECT_NAME}_node src/learning_msg_node.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"
# set_target_properties(${PROJECT_NAME}_node PROPERTIES OUTPUT_NAME node PREFIX "")

## Add cmake target dependencies of the executable
## same as for the library above
# add_dependencies(${PROJECT_NAME}_node ${${PROJECT_NAME}_EXPORTED_TARGETS} ${catkin_EXPORTED_TARGETS})

## Specify libraries to link a library or executable target against
# target_link_libraries(${PROJECT_NAME}_node
#   ${catkin_LIBRARIES}
# )

add_executable(msg_publisher src/msg_publisher.cpp) 
target_link_libraries(msg_publisher ${catkin_LIBRARIES}) 
add_dependencies(msg_publisher learning_msg_generate_messages_cpp) 

add_executable(msg_listener src/msg_listener.cpp) 
target_link_libraries(msg_listener ${catkin_LIBRARIES}) 
add_dependencies(msg_listener learning_msg_generate_messages_cpp)

#############
## Install ##
#############

# 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
# catkin_install_python(PROGRAMS
#   scripts/my_python_script
#   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_learning_msg.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)

五、编译并执行

在catkin_ws顶层目录中，运行

catkin_make

编译成功后生成可执行文件。然后，分别在三个终端中分别运行：
1）master管理节点

roscore

2）msg_publisher节点

rosrun learning_msg msg_publisher

3）msg_listener节点

rosrun learning_msg msg_listener

另开一终端，运行

rqt_graph

生成节点关系图：

文献：

[1] ROS教程（三）：创建程序包及节点（图文）