ros中NodeHandle類的subscribe()函數使用報錯問題

在使用ros寫訂閱者時，代碼如下：

#include "ros/ros.h"
#include "std_msgs/String.h"
#include <boost/thread.hpp>
#include <sensor_msgs/PointCloud2.h> 
#include <nav_msgs/Odometry.h> 
#include <typeinfo>

class multiThreadListener
{
public:
    void chatterCallback1(const nav_msgs::Odometry::ConstPtr &input_msg, std::string topicName);
    void chatterCallback2(const sensor_msgs::PointCloud2ConstPtr& input_msg, std::string topicName);
    multiThreadListener();

private:
    ros::NodeHandle n;
    std::string name1;
    std::string name2;
    ros::Subscriber sub1;
    ros::Subscriber sub2;
};

multiThreadListener::multiThreadListener()
{    
    name1 = "/navsat/odom";
    name2 = "/radar_cloud";
  
    sub1 = n.subscribe("/navsat/odom", 10, boost::bind(&multiThreadListener::chatterCallback1, this, _1, name1));
    sub2 = n.subscribe("/radar_cloud", 10, boost::bind(&multiThreadListener::chatterCallback2, this,_1, name2));
}

void multiThreadListener::chatterCallback1(const nav_msgs::Odometry::ConstPtr &input_msg, std::string topicName)
{
  ROS_INFO("I heard: [%s]", topicName);
  ros::Rate loop_rate(0.5);//block chatterCallback1()
  loop_rate.sleep();
}


void multiThreadListener::chatterCallback2(const sensor_msgs::PointCloud2ConstPtr& input_msg, std::string topicName)
{
  ROS_INFO("I heard: [%s]", topicName);
  ros::Rate loop_rate(0.5);//block chatterCallback2()
  loop_rate.sleep();
}
  

int main(int argc, char **argv)
{

  ros::init(argc, argv, "multi_sub");

  multiThreadListener listener_obj;
  ros::MultiThreadedSpinner s(2);
  ros::spin(s);

  return 0;
}

編譯總是報如下錯，

error: no matching function for call to ‘ros::NodeHandle::subscribe(const char [13], int, boost::_bi::bind_t<void, boost::_mfi::mf2<void, multiThreadListener, 
const boost::shared_ptr<const nav_msgs::Odometry_<std::allocator<void> > >&, std::__cxx11::basic_string<char> >, boost::_bi::list3<boost::_bi::value<multiThreadListener*>, 
boost::arg<1>, boost::_bi::value<std::__cxx11::basic_string<char> > > >)’  sub1 = n.subscribe("/navsat/odom", 10, boost::bind(&multiThreadListener::chatterCallback1, this, _1, name1));

原因是subscribe()函數在使用函數對象時，如boost::bind()函數返回的對象，必須要明確指定消息類型作為模板參數，因為編譯器無法推斷它。

上面就是沒有指明導致的錯誤。

在查看NodeHandle.h源碼查看subscribe()函數的定義如下

template<class M, class T>
Subscriber subscribe(const std::string& topic, uint32_t queue_size, void(T::*fp)(M), T* obj, const TransportHints& transport_hints = TransportHints())
{
     ...
}

template<class M, class T>
Subscriber subscribe(const std::string& topic, uint32_t queue_size, void(T::*fp)(const boost::shared_ptr<M const>&), T* obj, const TransportHints& transport_hints = TransportHints())
{
    ...
}

template<class M, class T>
Subscriber subscribe(const std::string& topic, uint32_t queue_size, void(T::*fp)(M), const boost::shared_ptr<T>& obj, const TransportHints& transport_hints = TransportHints())
{
    ...
}

template<class M, class T>
Subscriber subscribe(const std::string& topic, uint32_t queue_size, void(T::*fp)(const boost::shared_ptr<M const>&), const boost::shared_ptr<T>& obj, const TransportHints& transport_hints = TransportHints())
{
    ...
}

template<class M>
Subscriber subscribe(const std::string& topic, uint32_t queue_size, void(*fp)(M), const TransportHints& transport_hints = TransportHints())
{
    ...
}

template<class M>
Subscriber subscribe(const std::string& topic, uint32_t queue_size, void(*fp)(const boost::shared_ptr<M const>&), const TransportHints& transport_hints = TransportHints())
{
    ...
}

template<class M>
Subscriber subscribe(const std::string& topic, uint32_t queue_size, const boost::function<void (const boost::shared_ptr<M const>&)>& callback,
                           const VoidConstPtr& tracked_object = VoidConstPtr(), const TransportHints& transport_hints = TransportHints())
{
    ...
}

template<class M, class C>
Subscriber subscribe(const std::string& topic, uint32_t queue_size, const boost::function<void (C)>& callback,
                           const VoidConstPtr& tracked_object = VoidConstPtr(), const TransportHints& transport_hints = TransportHints())
{
    ...
}

很顯然，subscribe是模板函數，在傳入boost::function類型時，需要傳入模板參數，上面的代碼

sub2 = n.subscribe("/radar_cloud", 10, boost::bind(&multiThreadListener::chatterCallback2, this,_1, name2));

傳入了三個參數，第三個參數中的chatterCallback2()的第一個參數時sensor_msgs::PointCloud2ConstPtr，其定義是

typedef boost::shared_ptr< ::sensor_msgs::PointCloud2 const> sensor_msgs::PointCloud2ConstPtr

顯然，上面代碼使用的subscribe()函數是下面這個版本

template<class M>
Subscriber subscribe(const std::string& topic, uint32_t queue_size, const boost::function<void (const boost::shared_ptr<M const>&)>& callback,
                           const VoidConstPtr& tracked_object = VoidConstPtr(), const TransportHints& transport_hints = TransportHints())
{
    ...
}

故，正確的代碼應該如下

#include "ros/ros.h"
#include "std_msgs/String.h"
#include <boost/thread.hpp>
#include <sensor_msgs/PointCloud2.h> 
#include <nav_msgs/Odometry.h> 
#include <typeinfo>

class multiThreadListener
{
public:
    void chatterCallback1(const nav_msgs::Odometry::ConstPtr &input_msg, std::string topicName);
    void chatterCallback2(const sensor_msgs::PointCloud2ConstPtr& input_msg, std::string topicName);
    multiThreadListener();

private:
    ros::NodeHandle n;
    std::string name1;
    std::string name2;
    ros::Subscriber sub1;
    ros::Subscriber sub2;
};

multiThreadListener::multiThreadListener()
{    
    name1 = "/navsat/odom";
    name2 = "/radar_cloud";

    sub1 = n.subscribe<nav_msgs::Odometry>("/navsat/odom", 10, boost::bind(&multiThreadListener::chatterCallback1, this, _1, name1));
    sub2 = n.subscribe<sensor_msgs::PointCloud2>("/radar_cloud", 10, boost::bind(&multiThreadListener::chatterCallback2, this,_1, name2));
}

void multiThreadListener::chatterCallback1(const nav_msgs::Odometry::ConstPtr &input_msg, std::string topicName)
{
  ROS_INFO("I heard: [%s]", topicName);
  ros::Rate loop_rate(0.5);//block chatterCallback1()
  loop_rate.sleep();
}


void multiThreadListener::chatterCallback2(const sensor_msgs::PointCloud2ConstPtr& input_msg, std::string topicName)
{
  ROS_INFO("I heard: [%s]", topicName);
  ros::Rate loop_rate(0.5);//block chatterCallback2()
  loop_rate.sleep();
}
  

int main(int argc, char **argv)
{

  ros::init(argc, argv, "multi_sub");

  multiThreadListener listener_obj;
  ros::MultiThreadedSpinner s(2);
  ros::spin(s);

  return 0;
}

編譯通過。