How to subscribe to a camera and save image?

edit

Hi, So I am working with a car simulator and the car has simulated cameras attached to it. Now I am able to get a live video feed from the camera using rviz but I want to save the images that I am getting from the camera to be able to train my model using machine learning. I am not able to figure out how to save those images in a folder. I have tried many things that I found on the forums but nothing has really worked. I would really appreciate the help.

./testimage.cpp: line 6: syntax error near unexpected token `('
./testimage.cpp: line 6: `void imageCallback(const sensor_msgs::ImageConstPtr& msg)'

this was the error I got.

And this is what my code looks like:

#include <ros/ros.h>
 #include <image_transport/image_transport.h>
 #include <opencv2/highgui/highgui.hpp>
 #include <cv_bridge/cv_bridge.h>

void imageCallback(const sensor_msgs::ImageConstPtr& msg)
 {
   try
   {
     cv::imshow("view", cv_bridge::toCvShare(msg, "bgr8")->image);
     cv::waitKey(30);
   }
   catch (cv_bridge::Exception& e)
   {
     ROS_ERROR("Could not convert from '%s' to 'bgr8'.", msg->encoding.c_str());
   }
 }

 int main(int argc, char **argv)
 {
   ros::init(argc, argv, "image_listener");
   ros::NodeHandle nh;
   cv::namedWindow("view");
   cv::startWindowThread();
   image_transport::ImageTransport it(nh);
   image_transport::Subscriber sub = it.subscribe("/truevision/camera/front_right", 1, imageCallback);
   ros::spin();
   cv::destroyWindow("view");
 }