Requirements describe ： Coding implementation direction turtlesim Send a request , Generate a turtle at the specified position on the form of the turtle display node , This is a service request operation .
Result demonstration ：

Implementation process ：

• adopt ros Command to obtain service and service message information .
• Code the service request node .
• start-up roscore、turtlesim_node 、 Tortoise generates nodes , Generate new turtles .

1 Service name and service message acquisition

 Get the topic :/spawn：
	rosservice list
 Get message type :turtlesim/Spawn：
	rosservice type /spawn
 Get message format :
	rossrv info turtlesim/Spawn
	 In response to the results :
	float32 x
	float32 y
	float32 theta
	string name
	---
	string name

2 Service client implementation （C++）

To create a function package, you need to rely on the function package : roscpp rospy std_msgs turtlesim

/*  Make a little turtle   preparation : 1. Service topics  /spawn 2. Service message type  turtlesim/Spawn 3. Start before operation  turtlesim_node  node   Implementation process : 1. Include header file   Need to include  turtlesim  Resources under the package , Pay attention to  package.xml  To configure  2. initialization  ros  node  3. establish  ros  Handle  4. establish  service  client  5. Wait for the service to start  6. Send a request  7. Process response  */

#include "ros/ros.h"
#include "turtlesim/Spawn.h"

int main(int argc, char *argv[])
{
    
    setlocale(LC_ALL,"");
    // 2. initialization  ros  node 
    ros::init(argc,argv,"set_turtle");
    // 3. establish  ros  Handle 
    ros::NodeHandle nh;
    // 4. establish  service  client 
    ros::ServiceClient client = nh.serviceClient<turtlesim::Spawn>("/spawn");
    // 5. Wait for the service to start 
    // client.waitForExistence();
    ros::service::waitForService("/spawn");
    // 6. Send a request 
    turtlesim::Spawn spawn;
    spawn.request.x = 1.0;
    spawn.request.y = 1.0;
    spawn.request.theta = 1.57;
    spawn.request.name = "my_turtle";
    bool flag = client.call(spawn);
    // 7. Process response results 
    if (flag)
    {
    
        ROS_INFO(" New turtles are born , name :%s",spawn.response.name.c_str());
    } else {
    
        ROS_INFO(" Tortoise generation failed ！！！");
    }


    return 0;
}

3 function

• First , start-up roscore;
• Then start the tortoise display node ;
• Finally, start the tortoise to generate the request node ;
• The final execution result is similar to the demonstration result .