Hi, i am new to C++, i have done a couple of tutorials and know the basics(variables,func, class etc), but still need to learn in-depth concepts.
In the code below, can someone explain the concepts that are used, like say constructors, namespaces, etc, so that i can lean those topics in detail from online sources. You can skip the bare basics like variables, func etc, that any beginer would be familiar with.
I am at a stage where i don’t know what i don’t know (if you know what i mean ). Any help would be greatly appreciated. Ideally ,when answering,use to mention the code you are talking about for better readability.
Code 1:
#include <gazebo/gazebo.hh>
namespace gazebo
{
class WorldPluginTutorial : public WorldPlugin
{
public: WorldPluginTutorial() : WorldPlugin()
{
printf("Hello World!\n");
}
public: void Load(physics::WorldPtr _world, sdf::ElementPtr _sdf)
{
}
};
GZ_REGISTER_WORLD_PLUGIN(WorldPluginTutorial)
}
Code 2:
#include <thread>
#include "ros/ros.h"
#include "ros/callback_queue.h"
#include "ros/subscribe_options.h"
#include "std_msgs/Float32.h"
/// \brief A node use for ROS transport
private: std::unique_ptr<ros::NodeHandle> rosNode;
/// \brief A ROS subscriber
private: ros::Subscriber rosSub;
/// \brief A ROS callbackqueue that helps process messages
private: ros::CallbackQueue rosQueue;
/// \brief A thread the keeps running the rosQueue
private: std::thread rosQueueThread;
// Initialize ros, if it has not already bee initialized.
if (!ros::isInitialized())
{
int argc = 0;
char **argv = NULL;
ros::init(argc, argv, "gazebo_client",
ros::init_options::NoSigintHandler);
}
// Create our ROS node. This acts in a similar manner to
// the Gazebo node
this->rosNode.reset(new ros::NodeHandle("gazebo_client"));
// Create a named topic, and subscribe to it.
ros::SubscribeOptions so =
ros::SubscribeOptions::create<std_msgs::Float32>(
"/" + this->model->GetName() + "/vel_cmd",
1,
boost::bind(&VelodynePlugin::OnRosMsg, this, _1),
ros::VoidPtr(), &this->rosQueue);
this->rosSub = this->rosNode->subscribe(so);
// Spin up the queue helper thread.
this->rosQueueThread =
std::thread(std::bind(&VelodynePlugin::QueueThread, this));
/// \brief Handle an incoming message from ROS
/// \param[in] _msg A float value that is used to set the velocity
/// of the Velodyne.
public: void OnRosMsg(const std_msgs::Float32ConstPtr &_msg)
{
this->SetVelocity(_msg->data);
}
/// \brief ROS helper function that processes messages
private: void QueueThread()
{
static const double timeout = 0.01;
while (this->rosNode->ok())
{
this->rosQueue.callAvailable(ros::WallDuration(timeout));
}
}