How to publish integers values from a ROS node

edit

Hi to all,

I have a ROS node which publish data coming from encoders and current sensors (the node outputs velocity data, raw encoders ticks and currents). Currently, my ROS node publish all these data as std_msgs/String, but this gives me lot of problems when I need to handle data.

I would like to publish a structured ROS message which reports the robot status; what should I use for encoders ticks, velocity values and currents?

How should I re-write the code in order to implement a correct structured message? I think the best thing to do is to publish a topic for the velocity, another one for the motor current and another for the encoder ticks.

This is my current code, as you can see I declare everything like std_msgs::String.

Thank you for your help.

while (ros::ok())
  {

    std_msgs::String msg_sys, msg_enc, msg_io, msg_vel;
    std:string temp="", volt="", amotor="", enco="", aio="", dio=""; 
    std::stringstream ss, ss2, ss3, ssvel;          

    if (sys == 1){
      device.GetValue(_T, 0, temp);
      device.GetValue(_V, 0, volt);
      device.GetValue(_A, amotor);


      if (temp != "" && volt != "" && amotor != ""){

        std::replace(temp.begin(), temp.end(), ':', ',');
        std::replace(volt.begin(), volt.end(), ':', ',');
        std::replace(amotor.begin(), amotor.end(), ':', ',');

        ros::Time time = ros::Time::now();
        ss << time << "," << temp << "," << volt << "," << amotor << "," << count;
        msg_sys.data = ss.str();


        sys_pub.publish(msg_sys);
    }
  }

    //Encoder Topic
    if (enc == 1){
      current_time =ros::Time::now().toSec();
      device.GetValue(_C, 0, enco);
       //enco ="15000:16000";

      if (enco != ""){

        //Velocity 
        if (velocity == 1){
        std::string vel_enco=enco;
        std::replace(vel_enco.begin(), vel_enco.end(), ':', ' ');

        const char * c_enco = vel_enco.c_str();
        char* pEnd;
        double Encoder_sx, Encoder_dx;
        double Distance_sx, Distance_dx, Distance_prev_sx, Distance_prev_dx, Vel_sx, Vel_dx;
        float Vel_linear, w;

        Encoder_sx = std::strtod (c_enco,&pEnd);
        Encoder_dx = std::strtod (pEnd,&pEnd);

        Encoder_sx=Encoder_sx/pulse_rev_left;
        Encoder_dx=Encoder_dx/pulse_rev_right;
        Distance_sx = (Encoder_sx)*sprocket;
        Distance_dx = (Encoder_dx)*sprocket;

        last_time =ros::Time::now().toSec();
        Vel_sx = ((Distance_prev_sx - Distance_sx) / (last_time - current_time))/1000; // m / sec 
        Vel_dx = ((Distance_prev_dx - Distance_dx) / (last_time - current_time))/1000;  

        Distance_prev_sx = Distance_sx;
        Distance_prev_dx = Distance_dx;

        Vel_linear = (Vel_dx + Vel_sx)/2;
        w = (Vel_dx - Vel_sx)/track;

        ros::Time time2 = ros::Time::now();

        //Publish velocity topic
        ssvel << time2 << "," << Distance_sx << "," << Distance_dx << "," << Vel_sx << "," << Vel_dx << "," << Vel_linear << "," << w;
        msg_vel.data = ssvel.str();
        vel_pub.publish(msg_vel);
       }

        ros::Time time3 = ros::Time::now();

        std::replace(enco.begin(), enco.end(), ':', ',');

        //Publish enco topic
        ss2 << time3 << "," << enco << "," << count;
        msg_enc.data = ss2.str();
        enc_pub.publish(msg_enc);
      }
    }