05 ROS Parameter服务器实例

0.参数管理机制

1.Talker利用RPC通信向ROS MASTER发送参数及其数据，ROS MASTER将其保存在参数列表
2.Listener发送请求给ROS MASTER，查找已知参数名对应的参数值
3.ROS MASTER将参数值发送给Listener

1.建立功能包

catkin_create_pkg learning_parameter roscpp rospy std_srvs

2.编写源码

/*
Node Function:
Get Parameter from Parameter Server in ROSMASTER
*/

#include<string>
#include<ros/ros.h>
#include<std_srvs/Empty.h>

int main(int argc,char **argv)
{
   
    int red,green,blue;
    //ROS_INIT
    ros::init(argc,argv,"parameter_config");

    //NodeHandle_INIT
    ros::NodeHandle n;

    //Read background color Parameter and set variables
    ros::param::get("/turtlesim/background_r",red);
    ros::param::get("/turtlesim/background_b",blue);
    ros::param::get("/turtlesim/background_g",green);

    //Print INFO of current color
    ROS_INFO("Get backround Color[%d,%d,%d]",red,green,blue);

    //Set background color Parameter
    ros::param::set("/turtlesim/background_r",255);
    ros::param::set("/turtlesim/background_g",255);
    ros::param::set("/turtlesim/background_b",255);

    //Print INFO
    ROS_INFO("Set Background Color[255,255,255]");

    //Read background color Parameter again
    ros::param::get("/turtlesim/background_r",red);
    ros::param::get("/turtlesim/background_b",blue);
    ros::param::get("/turtlesim/background_g",green);

    //Print INFO of current color
    ROS_INFO("Get backround Color[%d,%d,%d]",red,green,blue);

    //Call Service /clear to refresh background
    ros::service::waitForService("/clear");
    ros::ServiceClient clear_background = n.serviceClient<std_srvs::Empty>("/clear");
    std_srvs::Empty srv;
    clear_background.call(srv);

    sleep(1);

    return 0;
}

clear_background.call(srv);

值得注意的是，在源码中，此处若无.call则报错如下

error: no match for call to ‘(ros::ServiceClient) (std_srvs::Empty&)’
47 | clear_background(srv);
| ^ make[2]: *** [learning_parameter/CMakeFiles/parameter_config.dir/build.make:63:
learning_parameter/CMakeFiles/parameter_config.dir/src/parameter_config.cpp.o] Error 1 make[1]: *** [CMakeFiles/Makefile2:1020:
learning_parameter/CMakeFiles/parameter_config.dir/all] Error 2 make:
*** [Makefile:141: all] Error 2

3.修改CMakeLists.txt

在build下添加

add_executable(parameter_config src/parameter_config.cpp)
target_link_libraries(parameter_config ${
   catkin_LIBRARIES})