Thread: Problem with callback as classmember

Hi,

I'm trying to call a callback as classmember, but what happens is all code being executed except the callback.

Code:

class Pera{
public:
Pera(ros::NodeHandle* _n):pos_x{
ROS_INFO("test 1");
ls_sub = n.subscribe("/gazebo/link_states", 1, &Pera::callback, this);
}

void callback(gazebo_msgs::Linkstates msgs_ls{
ROS_INFO("something");
}

....

};

At the moment, only "test 1" is printed, while "something" isnt. According to other examples I've found, there is a & missing in void callback, but when I put an & like

Code:

::LinkStates&

, it seems fine but compilation ends in error. Other solutions I've tried end in error as well. Can someone please help me?

Thank you.

I removed some printing code, but the structure is intact. Since I'm using specific libraries, I doubt you can instantly compile it.
Thanks for helping.

Code:

#include "ros/ros.h"
#include "gazebo_msgs/LinkStates.h"

using namespace std;

double twist_lin_x, twist_lin_y, twist_lin_z,
        pos_x, pos_y, pos_z,
        twist_ang_x, twist_ang_y, twist_ang_z,
        or_x, or_y, or_z, or_w,
        effort  = 0.0;
int loop = 0;
std_msgs::Float64 msg;

class Pera
{
public:
    Pera(ros::NodeHandle* _n):pos_x(0){
        //providing callback (a member) and a state (this)
        n = *_n;
        ROS_INFO("Subscribing to link_states");
        ls_sub = n.subscribe("/gazebo/link_states", 1, &Pera::callback, this);
        ROS_INFO("Subscribed");
    }

    void callback(gazebo_msgs::LinkStates msgs_ls){
            ROS_INFO("-------------------");
            ROS_INFO("Position x hand     : %.15lf", msgs_ls.pose[43].position.x);
            pos_x = msgs_ls.pose[43].position.x;
    }

    void run(){
        ROS_INFO("Declaring the right hand");
        std::string right_hand = (std::string)"amigo::hand_right";

        ROS_INFO("Advertising to set_link_state");
        ros::Publisher ls_pub = n.advertise<gazebo_msgs::LinkState>("/gazebo/set_link_state", 1);
        ROS_INFO("Creating instance");
        gazebo_msgs::LinkState linkState;

        ROS_INFO("Assigning link");
        linkState.link_name = right_hand;
        ROS_INFO("Assigning reference");
        linkState.reference_frame = right_hand;

        while (ros::ok())
        {
            ROS_INFO("Assigning pos x: %lf", pos_x);
            linkState.pose.position.x = pos_x;
        }
    }

protected:
    // state
    ros::NodeHandle n;
    ros::Subscriber ls_sub;
    double pos_x;
};

int main(int argc, char **argv)
{
    ROS_INFO("init");
    ros::init(argc, argv, "arm_joint_ik_receiver");
    ros::NodeHandle n;

    ROS_INFO("Calling PERA");
    Pera pera(&n);
    pera.run();
    ROS_INFO("Terminating");

    return 0;
}

Originally Posted by kmdv

n.subscribe() is called and a callback is passed, which means that n.subscribe() is the function which should call Pera::callback like this:

(ptr->*func)(msgs_ls)

where "ptr" is of type "Pera*", "func" is a pointer to Pera::callback,
and "msgs_ls" is your argument.

So you mean like Pera->*callback(msgs_ls) ? Can you give more information, because this doesn't compile for me..

Can you give more information, because this doesn't compile for me.

O_o

Nor should it.

That's also not what he said.

Soma

Originally Posted by phantomotap

Nor should it.

That's also not what he said.

So, since I apparently didn't get it, what did he say?

Originally Posted by kmdv

The bug probably lies inside ros::NodeHandle::subscribe(). You have to post code of that function.

That's a library I don't have the code of.

Do you know the difference between "passing a pointer to function" and "calling function pointed to by a pointer"?

Reading about it now...thank you

Thank you for the hint. Found the cause.