rosbag API c++ [closed]

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Hi all,

I'm writing a piece of code that is reading a bagfile, creating a new one, copying all the messages I'm interested from the old one to the new one, and adding a couple of topics more.

Until here everything is fine, but I would be able to copy all the messages from the old bagfile, without having to know the name of the topics and the type of message, but I can't find the way to do this with the C++ API...

I copy a piece of code just to illustrate the way my code works:

rosbag::Bag bag_read;
rosbag::Bag bag_write;
bag_read.open(old_bag, rosbag::bagmode::Read);
bag_write.open(new_bag, rosbag::bagmode::Write);

// First we copy all the topic we need to the new bagfile.

rosbag::View view_all(bag_read);    

BOOST_FOREACH(rosbag::MessageInstance const m, view_all){
    if (m.getTopic() == "/nav/odometry"){
            nav_msgs::Odometry::ConstPtr odom_msg = m.instantiate<nav_msgs::Odometry>();
            if (odom_msg != NULL){              
                ros::Time   time= m.getTime();
                bag_write.write("/nav/odometry", time, odom_msg);
            }
     }
    else if .... /* For every topic I'm interested on */

Thank you!!

SOLVED:

As Lorenz says there is no need to instantiate the message:

BOOST_FOREACH(rosbag::MessageInstance const m, view_all)
     bag_write.write(m.getTopic(),m.getTime(),m);