Having problem converting sensor_msgs:: Pointcloud2 to pcl

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Hello my friend,

I am trying to put point clouds gathered from Gazebo into PCL. The data format gathered from Block Laser is sensor_msgs::PointCloud, and I have managed to convert it to sensor_msgs::PointCloud2, but having problem convert it further into PCL Point cloud. My code is:

void scanCallback(const sensor_msgs::PointCloud scan)
{ 
    pcl::PointCloud<pcl::PointXYZ>::Ptr cloud(new pcl::PointCloud<pcl::PointXYZ>);
    sensor_msgs::PointCloud2 cloud2;
    sensor_msgs::convertPointCloudToPointCloud2(scan, cloud2); //point_cloud - msg::pt2
     pcl::fromPCLPointCloud2(cloud2,cloud);

}

where the last line complains an error which:

 error: no matching function for call to ‘fromPCLPointCloud2(sensor_msgs::PointCloud2&, pcl::PointCloud<pcl::PointXYZ>::Ptr&)

I have been struggling on this for quite a while, hopefully someone could very kindly point out the problem, cheers!