ROS话题中的发布和订阅

1.创建Publisher

Publisher的主要作用是针对制定话题发布特定数据类型的消息。我们用代码实现一个节点&＃xff0c;并且在节点中创建一个Publisher并发布字符串“Hello World”,代码如下&＃xff1a;

#include
#include "ros/ros.h"
#include "std_msgs/String.h"
int main(int argc, char **argv)
{
//ROS节点初始化
ros::init(argc,argv,"talker");
//创建节点句柄
ros::NodeHandle n;
//创建一个Publisher,发布名为chatter的topic,消息类型为std_msgs::String
ros::Publisher chatter_pub &＃61;n.advertise("chatter",1000);
//设置循环的频率
ros::Rate loop_rate(10);
int count &＃61; 0;
while (ros::ok())
{
// 初始化std_msgs::String类型的消息
std_msgs::String msg;
std::stringstream ss;
ss <<"hello world" <msg.data &＃61; ss.str();
//发布消息
ROS_INFO("%s",msg.data.c_str());
chatter_pub.publish(msg);
//循环等待回调函数
ros::spinOnce();
//按照循环频率延时
loop_rate.sleep();
&＃43;&＃43;count;
}
return 0;
}


2.创建Subscriber

下面创建一个Subscriber以订阅Publisher节点发布的“Hello World”字符串&＃xff0c;实现代码如下&＃xff1a;

#include "ros/ros.h"
#include "std_msgs/String.h"
//接收到订阅的消息后&＃xff0c;会进入消息回调函数
void chatterCallback(const std_msgs::String::ConstPtr& msg)
{
//将接收到的信息打印出来
ROS_INFO("I heard: [%s]",msg->data.c_str());
}
int main (int argc, char **argv)
{
//初始化ROS节点
ros::init(argc,argv,"listener");
//创建节点句柄
ros::NodeHandle n;
//创建一个Subscriber,订阅名为chatter的话题&＃xff0c;注册回调函数chatterCallback
ros::Subscriber sub&＃61;n.subscribe("chatter",1000,chatterCallback);
//循环等待回调函数
ros::spin();
return 0;
}


3.编译功能包

我们使用C&＃43;&＃43;语言来编写&＃xff0c;所以需要使用CMaker编译器进行编译&＃xff0c;编译规则通过功能包中的CMakerLists.txt文件设置&＃xff0c;使用catkin命令创建&＃xff0c;我们需要对部分内容进行更改&＃xff1b;

打开功能包中的CMakerLists.txt文件&＃xff0c;找到以下配置项&＃xff0c;去掉注释并稍作修改&＃xff1a;

## Specify additional locations of header files
## Your package locations should be listed before other locations
include_directories(
# include
${catkin_INCLUDE_DIRS}
)
##add_executable(hello ~/Alltest/catkin_ws/src/learning_communication/src/hello.cpp)
add_executable(talker src/talker.cpp)
target_link_libraries(talker ${catkin_LIBRARIES})
add_dependencies(talker ${PROJECT_NAME}_generate_messages_cpp)
add_executable(listener src/listener.cpp)
target_link_libraries(listener ${catkin_LIBRARIES})
add_dependencies(listener ${PROJECT_NAME}_generate_messages_cpp)


4.运行Publisher和Subscriber

在工作空间根目录设置环境变量并编译&＃xff1a;

source devel/setup.bash
catkin_make

a.启动ROS Master

roscore

b.启动Publisher

source devel/setup.bash
rosrun learning_communication talker

c.启动Subscriber

source devel/setup.bash
rosrun learning_communication listener

这样就运行起来了&＃xff0c;效果如下&＃xff1a;