ros introductory tutorial (seven) - Client Library (lower)

roscpp different demo demo

topic_demo

The basic model is similar, you can refer to the template.

Function Description: two Node, a release message simulated GPS (custom format, including coordinates and operating state), the message is accepted and processed further (to calculate the distance from the origin).

step:

1. package
2. msg
3. talker.cpp
4. listener.cpp
5. CMakeList.txt & package.xml

1. package

$ cd ~/catkin_ws/src
$ catkin_create_pkg topic_demo roscpp rospy std_msgs

2. msg

$ cd topic_demo/
$ mkdir msg
$ cd msg
$ vi gps.msg
# gps.msg
float32 x
float32 y
string state

When you finish creating msg, the compiler generates a ~/catkin_ws/devel/include/topic_demo/gps.hfile. Write code include into it

#include<topic_demo/gps.h>
topic_demo::gps msg;

3. talker.cpp

#include <ros/ros.h> 
#include <topic_demo/gps.h> 
int main(int argc, char** argv){
    ros::init(argc, argv, "talker" );    //解析参数，命名节点
    ros::NodeHandle nh;  //创建句柄， 实例化node
    topic_demo::gps msg;  //创建gps消息
    msg.x = 1.0;
    msg.y = 1.0;
    msg.state = "working";
    ros::Publisher pub = nh.advertise<topic_demo::gps>("gps_info", 1);  //用句柄操作创建publisher，<需要publish的类型>
    ros::Rate loop_rate(1.0);   //定义循环发布的频率
    while(ros::ok()){
        msg.x = 1.03 * msg.x;
        msg.y = 1.01 * msg.y;
        ROS_INFO( "Talker: GPS: x = %f, y = %f", msg.x , msg.y);
        pub.publish(msg);  //发布消息
        loop_rate.sleep();  
    }
    return 0；
}

4. listener.cpp

#include <ros/ros.h>
#include <topic_demo/gps.h>
#include <std_msgs/Float32.h>

void gpsCallback(const topic_demo::gps::ConstPtr &msg)  //ConstPtr &msg定义于gps.h文件中
{
    std_msgs::Float32 distance;
    distance.data = sqrt(pow(msg ->x, 2), pow(msg -> y, 2));
    ROS_INFO( " Listener: Distance to origin = %f, state = %s" , distanace.data, msg -> state.c_str() );
 }
int main(int argc, char** argv){
    ros::init(argc, argv, " listener");
    ros::NodeHandle n;
    ros::Subscribe sub = n.subscribe( "gps_info", 1, gpsCallback);  // 'gpsCallback'为该回调函数的指针，接受到消息后会通过该函数处理
    ros::spin();  //反复调用当前可触发的回调函数（阻塞） 
    return 0;
}

Tips: ros :: spinOnce () action with spin, but it is non-blocking.

5. CMakeLists.txt

Then you can compile (catkin_make) and run (rosrun) a ~

service_demo

The basic model is similar, you can refer to the template.

Function Description: two Node, a release request (custom format), other receive and process the message and return information.

step:

1. package
2. msg
3. server.cpp
4. client.cpp
5. CMakeList.txt & package.xml

1. package

$ cd ~/catkin_ws/src
$ catkin_create_pkg service_demo roscpp rospy std_msgs

2. srv

$ cd service_demo/
$ mkdir srv
$ vi Greeting.srv
# Greeting.srv
string name
int32 age 
---
string feedback

When you finish creating srv, the compiler generates ~/catkin_ws/devel/include/service_demo/Greeting.h, .../GreetingRequest.h, .../GreetingResponse.hfile. Write code include into it

3. server.cpp

#include <ros/ros.h> 
#include <service_demo/Greeting.h> 

bool handle_function(service::demo::Greeting::Request &req, service::demo::Greeting::Response &res){
    //显示请求信息
    ROS_INFO( "Request from %s with age %d" . req.name.c_str(), req.age();
    //处理请求，结果写入response
    res.feedback = "Hi" + req.name + ". I' m server!" '
    //返回true，正确处理了请求
    return true;
}
int main(int argc, char** argv){
    ros::init(argc, argv, "greetings_server" );    //解析参数，命名节点
    ros::NodeHandle nh;  //创建句柄， 实例化node
    ros::ServiceServer service = nh.advertiseService("greetings",handle_function); //提供服务，后者同样是函数指针。
    ros::spin();
    return 0;
}

4. client.cpp

#include <ros/ros.h>
#include <service_demo/Greeting.h>

int main(int argc, char** argv){
    ros::init(argc, argv, " greetings_server" ); //解析参数，命名节点
    ros::NodeHandle nh;
    ros::ServiceClient client = nh.serviceClient<service_demo::Greeting>( "greetings" ); //“greetings”是发送的服务名
    
    service_demo::Greeting srv;
    srv.request.name = "HAN" ; 
    srv.request.age = "20" ; 
    
    if (client.call(srv)){  //call 的返回值就是上面Handle_function 的返回值。
        ROS_INFO( " Feedback from server : %s." , srv.response.feedback );
    }
    else{
        ROS_ERROR ( "Failed to call service greetings.") ; 
        return 1;
    }
    
    return 0;
    
}

5. CMakeLists.txt & package.xml

Then you can compile (catkin_make) and run (rosrun) a ~

param_demo

Two kinds of API: ros :: param and ros :: NodeHandle

Setting the parameters of ways:

• In the code

#include <ros/ros.h>
int main(int argc, char** argv){
    ros::init(argc,argv, "greetings_server");
    ros::NodeHandle nh;
    int param1, param2, param3, param4, param5;
    //获取参数
    ros::param::get ("param1", param1);
    nh.getParam ("param2", param2);
    nh.param ("param3", param3, 123); //123是默认值
    //设置参数
    ros::param::set( "param4" , param4);
    nh.setParam("param5", param5);
    //检查参数是否存在
    ros::param::has("param5");
    nh.hasParam("param6");
    //删除参数
    ros::param::del("param5");
    nh.deleteParam("param6");
    
    return 0;
    
}

• In the launch file
  

Please indicate the source.
This paper summarizes the Chinese University of MOOC "Android OS Getting Started"
link: Link .
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