‘this’ argument discards qualifiers [-fpermissive]

Question

This is my code for the Adaptive Monte Carlo localization(AMCL) algorithm using ROS.

#include <ignition/plugin/Register.hh>
#include <ignition/gazebo/Model.hh>
#include <ignition/gazebo/EntityComponentManager.hh>
#include <ignition/gazebo/Util.hh>
#include <ignition/gazebo/System.hh>


//ROS libraries
#include <ros/ros.h>
#include <ros/callback_queue.h>

// Dependencies
#include <geometry_msgs/PoseWithCovarianceStamped.h>
#include <tf2_ros/transform_listener.h>
#include <geometry_msgs/TransformStamped.h>

// STL
#include <memory>
#include <thread>
#include <string>


using namespace ignition;
using namespace gazebo;
using namespace systems;

////////////////////////////////////////////////////////////////////////////

class ignition::gazebo::systems::amclPrivate
{
    public: Model model{kNullEntity};

    public: bool updateAmclPose(const UpdateInfo &_info,
                                const EntityComponentManager &_ecm);

};

/////////////////////////////////////////////////////////////////////////////

amcl::amcl() : 
  System(), dataPtr(std::make_unique<amclPrivate>())

{
   tfListener_(tfBuffer_)
}

/////////////////////////////////////////////////////////////////////////////

amcl::~amcl() = default;
{
  // Disable callback queue
  amcl_queue_.clear();
  amcl_queue_.disable();

  // Shutdown ROS node handle
  amcl_nh_.shutdown();

  // Wait for child thread to join
  if(thread_ptr_->joinable())
    thread_ptr_->join();
}

/////////////////////////////////////////////////////////////////////////////

void amcl::Configure(const Entity &_entity,
    const std::shared_ptr<const sdf::Element> &_sdf,
    EntityComponentManager &_ecm,
    EventManager &_eventMgr)

{
    this->dataPtr->model = Model(_entity);
    if (!this->dataPtr->model.Valid(_ecm))
    {
    
    ignerr << "amcl plugin should be attached to a model entity. "
           << "Failed to initialize." << std::endl;
    return;
    }
    
    // Obtain parameters from xacro file

    if(_sdf->HasElement("topicRate"))
    {
        rate_ = _sdf->GetElement("topicRate")->Get<double>(); ########################line 95 

    }
    else
    {
      rate_ = 10.0;
    }


    if(_sdf->HasElement("fixedFrame"))
    
    {
        fixed_frame_ = _sdf->GetElement("fixedFrame")->Get<std::string>(); ############################line 107
        
    }
    else
    {
        fixed_frame_ = "map";
    }

    if(_sdf->HasElement("robotFrame"))
        
    {
        robot_frame_ = _sdf->GetElement("robotFrame")->Get<std::string>(); ######################line 118
        
    }
    else
    {
        robot_frame_ = "base_link";
    }

    // Ensure that ROS node for Gazebo has been initialized
    if(!ros::isInitialized())
    {
        int argc = 0; char ** argv = NULL;
        ros::init(argc, argv, "ignition_gazebo_robot", ros::init_options::NoSigintHandler);
    }

    // Set callback queue

    amcl_nh_.setCallbackQueue(& amcl_queue_);
    amcl_pub_ = amcl_nh_.advertise<geometry_msgs::PoseWithCovarianceStamped>("amcl",1,true);

    thread_ptr_ = std::make_shared<std::thread>([this]()
            {
                // Set process rate
                ros::Rate r(this->rate_);
                while (this->amcl_nh_.ok())
                {
                    this->updateAmclPose(const UpdateInfo &_info,
                         const EntityComponentManager &_ecm);

                    this->amcl_pub_.publish(this->msg_);

                    this->amcl_queue_.callAvailable(ros::WallDuration(0.0));

                    r.sleep();
                }
            }
        

            // Notify plugin status
        ROS_INFO_STREAM(
            ros::this_node::getName() << " plugin amcl pose successfully loaded."
        );

}
//////////////////////////////////////////////////////////////////////////////////////

void amcl::PreUpdate(const ignition::gazebo::UpdateInfo &_info,
                     ignition::gazebo::EntityComponentManager &_ecm)
{
  IGN_PROFILE("amcl::PreUpdate");


  if (_info.dt < std::chrono::steady_clock::duration::zero())
  {
    ignwarn << "Detected jump back in time ["
        << std::chrono::duration_cast<std::chrono::seconds>(_info.dt).count()
        << "s]. System may not work properly." << std::endl;
  }



///////////////////////////////////////////////////////////////////////////////////////

void amcl::PostUpdate(const ignition::gazebo::UpdateInfo &_info,
                      ignition::gazebo::EntityComponentManager &_ecm)

{
  IGN_PROFILE("amcl::PostUpdate");
  // Nothing left to do if paused.
  if (_info.paused)
  
    return;
  
  this->dataPtr->updateAmclPose(const UpdateInfo &_info,const EntityComponentManager &_ecm)



///////////////////////////////////////////////////////////////////////////////////////

bool amcl::updateAmclPose(const UpdateInfo &_info,
                         const EntityComponentManager &_ecm)
{
  
  IGN_PROFILE("amcl::updateAmclPose");

  bool isok {false};

  try
        
  {
      if(tfBuffer_.canTransform(fixed_frame_, robot_frame_, ros::Time(0)))
        
      {
          read_transformation_ = tfBuffer_.lookupTransform(fixed_frame_, robot_frame_, ros::Time(0), ros::Duration(60.0));

          msg_.header.frame_id = fixed_frame_;
          msg_.header.stamp = ros::Time::now();

          msg_.pose.pose.position.x = read_transformation_.transform.translation.x;
          msg_.pose.pose.position.y = read_transformation_.transform.translation.y;
          msg_.pose.pose.position.z = read_transformation_.transform.translation.z;

          msg_.pose.pose.orientation.x = read_transformation_.transform.rotation.x;
          msg_.pose.pose.orientation.y = read_transformation_.transform.rotation.y;
          msg_.pose.pose.orientation.z = read_transformation_.transform.rotation.z;
          msg_.pose.pose.orientation.w = read_transformation_.transform.rotation.w;
      }
      isok = true;
        
   } 
   catch(const tf2::TimeoutException & e)
        
   {
        
        ROS_ERROR_STREAM(
            ros::this_node::getName() << " " << __func__ <<
            " timeout exception: " << e.what()
        );    
        return isok;

    }
        
    catch(const tf2::TransformException & e)
        
    {
        ROS_ERROR_STREAM(
            ros::this_node::getName() << " " << __func__ <<
            " transform exception: " << e.what()
        );
        
        return isok;
    }

    return isok;
    
    }
 }

 }

Error (in line 95, 107 and 118)

error: passing ‘std::__shared_ptr_access<const sdf::v9::Element, (__gnu_cxx::Lock_policy)2, false, false>::element_type’ {aka ‘const sdf::v9::Element’} as ‘this’ argument discards qualifiers [-fpermissive] rate = _sdf->GetElement("topicRate")->Get();

Complete error (as shown in the terminal)

/home/adwaitnaik/plugin_ws/src/amcl/Amcl.cc: In member function ‘virtual void ignition::gazebo::v3::systems::amcl::Configure(const Entity&, const std::shared_ptr&, ignition::gazebo::v3::EntityComponentManager&, ignition::gazebo::v3::EventManager&)’: /home/adwaitnaik/plugin_ws/src/amcl/Amcl.cc:95:45: error: passing ‘std::__shared_ptr_access<const sdf::v9::Element, (__gnu_cxx::Lock_policy)2, false, false>::element_type’ {aka ‘const sdf::v9::Element’} as ‘this’ argument discards qualifiers [-fpermissive] rate = _sdf->GetElement("topicRate")->Get(); ^ In file included from /usr/include/ignition/gazebo3/ignition/gazebo/System.hh:28, from /home/adwaitnaik/plugin_ws/src/amcl/Amcl.hh:18, from /home/adwaitnaik/plugin_ws/src/amcl/Amcl.cc:10: /usr/include/sdformat-9.5/sdf/Element.hh:330:24: note: in call to ‘sdf::v9::ElementPtr sdf::v9::Element::GetElement(const string&)’ public: ElementPtr GetElement(const std::string &_name); ^~~~~~~~~~ /home/adwaitnaik/plugin_ws/src/amcl/Amcl.cc:107:53: error: passing ‘std::__shared_ptr_access<const sdf::v9::Element, (__gnu_cxx::Lock_policy)2, false, false>::element_type’ {aka ‘const sdf::v9::Element’} as ‘this’ argument discards qualifiers [-fpermissive] fixed_frame = _sdf->GetElement("fixedFrame")->Getstd::string(); ^ In file included from /usr/include/ignition/gazebo3/ignition/gazebo/System.hh:28, from /home/adwaitnaik/plugin_ws/src/amcl/Amcl.hh:18, from /home/adwaitnaik/plugin_ws/src/amcl/Amcl.cc:10: /usr/include/sdformat-9.5/sdf/Element.hh:330:24: note: in call to ‘sdf::v9::ElementPtr sdf::v9::Element::GetElement(const string&)’ public: ElementPtr GetElement(const std::string &_name); ^~~~~~~~~~ /home/adwaitnaik/plugin_ws/src/amcl/Amcl.cc:118:53: error: passing ‘std::__shared_ptr_access<const sdf::v9::Element, (__gnu_cxx::Lock_policy)2, false, false>::element_type’ {aka ‘const sdf::v9::Element’} as ‘this’ argument discards qualifiers [-fpermissive] robot_frame = _sdf->GetElement("robotFrame")->Getstd::string(); ^

The line is marked in the code.

I referred to this link but couldn't get the solution

Can anybody suggest a workaround?

PS: I got the same error for line 107 and 118 (marked in code with '#######')

Please try to create a [mcve] to show us, with emphasis on the *minimal* part. — Some programmer dude, Apr 07 '21 at 14:17
`amcl::~amcl() = default; {.....` did you notice that you default the destructor, but still provide an implementation? — JHBonarius, Apr 07 '21 at 14:24
@Adwait The error message says that `GetElement` isn't const; it gives the prototype as `ElementPtr GetElement(const std::string &_name);` — molbdnilo, Apr 07 '21 at 14:34

score 0 · Answer 1 · answered Apr 07 '21 at 16:18

To understand the proposed changes, one should have some familiarity with concepts related to ignition gazebo

change Line 95, 107, 118 with the following lines

auto rate_ = _sdf->Get<double>("topicRate"); //line 95

auto fixed_frame_ = _sdf->Get<std::string>("fixedFrame"); //107

auto robot_frame_ = _sdf->Get<std::string>("robotFrame"); //118

Possible explanation

Refer this

‘this’ argument discards qualifiers [-fpermissive]

1 Answers1