Communicating using receiver node in webots

I want to implement an emitter robot and a receiver robot in webots. I have written following code.

#include <webots/robot.h>
#include <webots/receiver.h>

#include <stdio.h>
#include <math.h>

#define TIME_STEP 64

int main(int argc, char **argv) {
  /* necessary to initialize webots stuff */
  wb_robot_init();
  WbDeviceTag rx = wb_robot_get_device("receiver");
  wb_receiver_enable(rx, 64);
  printf("Receiver sampling period: %d",wb_receiver_get_sampling_period(rx));
  
  while (wb_robot_step(TIME_STEP) != -1) {
    
    if (wb_receiver_get_queue_length(rx) > 0) {
      const char *message = wb_receiver_get_data(rx);
      const double *dir = wb_receiver_get_emitter_direction(rx);
      double signal = wb_receiver_get_signal_strength(rx);
      printf("received: %s (signal=%g, dir=[%g %g %g])\n",
             message, signal, dir[0], dir[1], dir[2]);
      wb_receiver_next_packet(rx);
    }
  };

  /* Enter your cleanup code here */

  /* This is necessary to cleanup webots resources */
  wb_robot_cleanup();

  return 0;
}

It compiles successfully. But when I execute it, it generate following result,

Error: wb_receiver_enable(): invalid device tag. Error: wb_receiver_get_sampling_period(): invalid device tag.

How can I fix this error?

I want to receive the message emitted by emitter

Solution

This error shows up because there is no device named "receiver" in your Robot node. What kind of robot are using? If it is a Robot node defined in the world file (.wbt), you should add to the children list of your Robot node a Receiver node named "receiver" (which is the default name). If you are using a PROTO-based robot, like E-Puck or Nao, you should check whether the proto file already contains a Receiver node and use its name instead of "receiver". If it doesn't contain any Receiver node, you should be able to add a Receiver node in some extensionSlot of the robot.

The very same principle applies to the Emitter node as well.