ROS是基于topic发布和订阅来实现通信，底层是TCP来发送消息，具体原理本文不在详细介绍。本文将手动实现两个ros节点的通信。

首先进入ROS，并进入/catkin_ws/src目录

创建新的package

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1	catkin_create_pkg basic_topic roscpp std_msgs

#向功能包添加自定义消息文件(.msg)

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roscd custom_msg_topic
mkdir msg && cd msg
gedit custom_msg.msg

在custom_msg.msg文件中输入如下的内容：

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string first_name
string last_name
uint8 age
string character

修改CMakeLists.txt文件的内容为：

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cmake_minimum_required(VERSION 2.8.3)
project(custom_msg_topic)
find_package(catkin REQUIRED COMPONENTS
  roscpp
  std_msgs
  message_generation
)
add_message_files(
  FILES
  custom_msg.msg
)
generate_messages(
  DEPENDENCIES
  std_msgs
)
catkin_package(
  LIBRARIES custom_msg_topic
  CATKIN_DEPENDS roscpp message_runtime
)
include_directories(
  ${catkin_INCLUDE_DIRS}
)

回到功能包所在的工作空间，构建功能包:

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1 2	cd ~/catkin_ws catkin_make

编译之后会在include文件夹下生成对应的custom_msg.h文件
可以来检测一下

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ros@sunxin-ThinkPad-T480s.master> rosmsg show custom_msg_topic/custom_msg
string first_name
string last_name
uint8 age
string character

生成了自定义的消息头文件之后，我们就可以利用自定义的消息格式来编写节点了.

建立publisher节点

一般包含如下要素:
ROS节点初始化
创建节点句柄
穿件publisher
设置循环频率

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1 2	roscd custom_msg_topic/src gedit custom_msg_publisher.cpp

并编辑cpp文件加入以下代码（代码具体讲解参考文下参考文献）

c++

#include "ros/ros.h"
#include "custom_msg_topic/custom_msg.h"
#include <sstream>
int main(int argc, char **argv)
{
  ros::init(argc, argv, "custom_msg_publisher");
  ros::NodeHandle nh;
  ros::Publisher custom_msg_pub = nh.advertise<custom_msg_topic::custom_msg>("test", 100);
  ros::Rate loop_rate(10);
  while (ros::ok())
  {
    custom_msg_topic::custom_msg msg;
    std::stringstream ss;
    ss<<"Xiao Xin";
    ss>>msg.last_name; 
    ss>>msg.first_name; 
    msg.age = 18;
    msg.character = "lovely";

    custom_msg_pub.publish(msg);
    loop_rate.sleep();
  }
  return 0;
}

#建立subsriber节点
一般包含如下要素:

回调函数
ROS节点初始化
创建节点句柄
穿件publisher
循环等待回调函数

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1 2	roscd custom_msg_topic/src gedit custom_msg_subscriber.cpp

c++

#include "ros/ros.h"
#include "custom_msg_topic/custom_msg.h"

void test_infoCallback(const custom_msg_topic::custom_msgConstPtr &msg)
{
  ROS_INFO("I heard: [%s %s]", msg->last_name.c_str(), msg->first_name.c_str());
  ROS_INFO("his age is: [%d]; and he is [%s]", msg->age, msg->character.c_str());
}

int main(int argc, char **argv)
{
  ros::init(argc, argv, "custom_msg_subscriber");
  ros::NodeHandle nh;
  ros::Subscriber sub = nh.subscribe("test", 1000, test_infoCallback);

  ros::spin();
  return 0;
}

修改功能包的CMakeLists.txt文件

打开终端

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1 2	roscd custom_msg_topic gedit CMakeLists.txt

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cmake_minimum_required(VERSION 2.8.3)
project(custom_msg_topic)
find_package(catkin REQUIRED COMPONENTS
  roscpp
  std_msgs
  message_generation
)
add_message_files(
  FILES
  custom_msg.msg
)
generate_messages(
  DEPENDENCIES
  std_msgs
)
catkin_package(
  LIBRARIES custom_msg_topic
  CATKIN_DEPENDS roscpp message_runtime
)
include_directories(
  ${catkin_INCLUDE_DIRS}
)

# 下面是需要添加的内容
add_executable(custom_msg_publisher src/custom_msg_publisher.cpp)
add_executable(custom_msg_subscriber src/custom_msg_subscriber.cpp)
add_dependencies(custom_msg_publisher ${${PROJECT_NAME}_EXPORTED_TARGETS} ${catkin_EXPORTED_TARGETS})
add_dependencies(custom_msg_subscriber ${${PROJECT_NAME}_EXPORTED_TARGETS} ${catkin_EXPORTED_TARGETS})
target_link_libraries(custom_msg_publisher ${catkin_LIBRARIES})
target_link_libraries(custom_msg_subscriber ${catkin_LIBRARIES})