Hi, I am a ROS beginner and this might seem like a silly doubt but I haven't found the solution on the forums yet.

I have a robot which is localizing using AMCL. I wish to write a subscriber that can subscribe to the amcl_pose topic and read the geometry_msgs/PoseWithCovarianceStamped to be used somewhere else.

This is the code that I have for now but I am receiving a lot of errors but I am unclear on what is going wrong

#include "ros/ros.h"
#include "geometry_msgs/PoseWithCovarianceStamped.h"
double poseAMCLx, poseAMCLy, poseAMCLa;
void poseAMCLCallback(const geometry_msgs::PoseWithCovarianceStamped::ConstPtr& msgAMCL)
{
    poseAMCLx = msgAMCL->pose.pose.position.x;
    poseAMCLy = msgAMCL->pose.pose.position.y;
    poseAMCLa = msgAMCL->pose.pose.orientation.w;   
    //ROS_INFO(msgAMCL);
}

int main(int argc, char **argv)
{
    ros::init(argc, argv, "err_eval");
    ros::NodeHandle n;
    ros::Subscriber sub_amcl = n.subscribe<geometry_msgs::PoseWithCovarianceStamped>("amcl_pose", poseAMCLCallback);
    ros::Rate loop_rate(10);
    ros::spinOnce();

    int count = 0;
    while (ros::ok())
    {

        geometry_msgs::Pose error;
        error.position.x = poseAMCLx;
        error.position.y = poseAMCLy;
        error.orientation.w = poseAMCLa;
        pub.publish(error);

        ros::spinOnce();
        loop_rate.sleep();
        count=count+1;
    }

    return 0;
}

`