requires ‘template<>’ syntax --> Call Class Template via a function - c++

Question

I have a header class that looks like this:
#ifndef A_H__
#define A_H__
using namespace pcl::tracking;
namespace ball_tracking_cloud
{
template <typename PointType>
class OpenNISegmentTracking
{
public:
//...
protected:
void update(const sensor_msgs::PointCloud2ConstPtr &input_cloud);
}; // end of class
} // end namespace
#endif
And now I have a .cpp file that looks like this:
#include <ball_tracking_cloud/particle_detector.h>
bool init = true;
namespace ball_tracking_cloud
{
void OpenNISegmentTracking<pcl::PointXYZRGBA>::update(const sensor_msgs::PointCloud2ConstPtr &input_cloud)
{
pcl::PointCloud<pcl::PointXYZRGBA>::Ptr cloud(new pcl::PointCloud<pcl::PointXYZRGBA>);
pcl::fromROSMsg(*input_cloud, *cloud);
if(init)
{
v.run ();
init=false;
}
v.cloud_cb(cloud);
}
} // end of namespace
If I compile my code I get this error:
: error: specializing member ‘ball_tracking_cloud::OpenNISegmentTracking<pcl::PointXYZRGBA>::update’ requires ‘template<>’ syntax
void OpenNISegmentTracking<pcl::PointXYZRGBA>::update(const sensor_msgs::PointCloud2ConstPtr &input_cloud)
^
/hri/localdisk/markus/ros-alex/src/ball_tracking/ball_tracking_cloud/src/particle_detector.cpp:38:1: error: expected ‘}’ at end of input
} // end of namespace
^
I am not sure why I get this error..... I guess it has something to do with the fact that I use a template class ..... but I am not sure about this....
Any help would be great!

Answer 1

Your OpenNISegmentTracking is what in c++ terms is called a full template specialization.
In other words, it's a version of your template that will be invoked, only when the template parameter is a pcl::PointXYZRGBA.
The proper syntax for such a definition is
template <>
void OpenNISegmentTracking<pcl::PointXYZRGBA>::update(const sensor_msgs::PointCloud2ConstPtr &input_cloud)
{
...
}

Answer 2

You need this syntax for the function name:
template<>
void OpenNISegmentTracking<pcl::PointXYZRGBA>::update(const sensor_msgs::PointCloud2ConstPtr &input_cloud)
{
// ...
}