ROS系统 通过服务编程实现两个数相加并返回

Posted 2021-08-08 ʚVVcatɞ

创建功能包

cd ~/catkin_ws/src

catkin_create_pkg learning_communication roscpp rospy std_msgs geometry_msgs turtlesim

定义 srv 文件

cd ~/catkin_ws/src/learning_communication

mkdir srv

创建 AddTwoInts.srv 文件

cd ~/catkin_ws/src/learning_communication/srv

touch AddTwoInts.srv

AddTwoInts.srv 文件内容

int64 a
int64 b
---
int64 sum

在package.xml中添加功能包依赖

<build_depend>message_generation</build_depend>
<exec_depend>message_runtime</exec_depend>

在CMakeLists.txt添加编译选项

find_package(catkin REQUIRED COMPONENTS
  ......
  ......
  message_generation 
)

catkin_package(
#  INCLUDE_DIRS include
#  LIBRARIES learning_topic
  CATKIN_DEPENDS geometry_msgs roscpp rospy std_msgs turtlesim message_runtime
#  DEPENDS system_lib
)

add_service_files(FILES AddTwoInts.srv)
generate_messages(DEPENDENCIES std_msgs)

配置完成后，对工程目录进行编译

cd ~/catkin_ws

catkin_make

通过以下代码去调用生成的头文件

在 src 目录下创建 两个 cpp文件

cd ~/catkin_ws/src/learning_communication/src

创建 server.cpp 文件

touch server.cpp

以下是server.cpp 文件中的内容
代码功能：将输入参数中的请求数据相加，结果放到应答变量中

#include <ros/ros.h>
#include "learning_communication/AddTwoInts.h"

// service回调函数，输入参数req，输出参数res
bool add(learning_communication::AddTwoInts::Request  &req,
         			learning_communication::AddTwoInts::Response &res)
{
    // 将输入参数中的请求数据相加，结果放到应答变量中
	res.sum = req.a + req.b;
	ROS_INFO("request: x=%ld, y=%ld", (long int)req.a, (long int)req.b);
	ROS_INFO("sending back response: [%ld]", (long int)res.sum);
	
    return true;
}

int main(int argc, char **argv)
{
    // ROS节点初始化
    ros::init(argc, argv, "add_two_ints_server");

    // 创建节点句柄
    ros::NodeHandle n;

    // 创建一个名为/show_person的server，注册回调函数personCallback
    ros::ServiceServer service = n.advertiseService("/add_two_ints", add);

    // 循环等待回调函数
    ROS_INFO("Ready to add two ints.");
    ros::spin();

    return 0;
}

创建 client.cpp 文件

touch client.cpp

client.cpp 文件中的内容
代码功能：发布service请求，等待加法运算的应答结果

#include <cstdlib>
#include <ros/ros.h>
#include "learning_communication/AddTwoInts.h"

int main(int argc, char** argv)
{
    // 初始化ROS节点
	ros::init(argc, argv, "add_two_ints_client");
	
	// 从终端命令行获取两个加数
	if (argc != 3){
		ROS_INFO("usage: add_two_ints_client X Y");
		return 1;
	}

    // 创建节点句柄
	ros::NodeHandle n;

    // 创建一个client，请求add_two_int service, service消息类型是 learning_communication::AddTwoInts
	ros::ServiceClient client = n.serviceClient<learning_communication::AddTwoInts>("add_two_ints");

    // 创建learning_communication::AddTwoInts类型的service消息
	learning_communication::AddTwoInts srv;
	srv.request.a = atoll(argv[1]);
	srv.request.b = atoll(argv[2]);

    // 发布service请求，等待加法运算的应答结果
	if (client.call(srv)){
		ROS_INFO("Sum: %ld", (long int)srv.response.sum);
	}else{
		ROS_ERROR("Failed to call service add_two_ints");
		return 1;
	}
	
	return 0;
};

在CMakeLists.txt文件中添加以下代码：

add_executable(server src/server.cpp)
target_link_libraries(server ${catkin_LIBRARIES})
add_dependencies(server ${PROJECT_NAME}_gencpp)

add_executable(client src/client.cpp)
target_link_libraries(client ${catkin_LIBRARIES})
add_dependencies(client ${PROJECT_NAME}_gencpp)

编译工程项目

cd ~/catkin_ws

catkin_make

启动ROS Master

roscore

启动自定义的订阅者节点

rosrun learning_communication server

启动自定义的发布者节点

rosrun learning_communication client 7 8

Client启动后发布服务请求，并成功接收到反馈结果。

Server接收到服务调用后完成加法求解，并将结果反馈给Client。