How to compile a c++ code using libtorrent?

Question

I am testing the example code posted on the official libtorrent website (https://www.libtorrent.org/tutorial-ref.html). I pasted the code here:

#include <libtorrent/session.hpp>
#include <libtorrent/add_torrent_params.hpp>
#include <libtorrent/torrent_handle.hpp>
#include <libtorrent/magnet_uri.hpp>

int main(int argc, char const* argv[])
{
        if (argc != 2) {
                fprintf(stderr, "usage: %s <magnet-url>\n");
                return 1;
        }
        lt::session ses;

        lt::add_torrent_params atp = lt::parse_magnet_uri(argv[1]);
        atp.save_path = "."; // save in current dir
        lt::torrent_handle h = ses.add_torrent(atp);

        // ...
}

I have already installed the libtorrent:

ldconfig -v | grep libtorrent
libtorrent-rasterbar.so.9 -\> libtorrent-rasterbar.so.9.0.0

I used the following command to compile the code:

g++ main.cpp -o run -ltorrent-rasterbar -lboost_filesystem-mt

However, I got errors:

main.cpp: In function 'int main(int, const char\*\*)':
main.cpp:12:3: error: 'lt' has not been declared
lt::session ses;

I also saw another solution, but it does not resolve the issue I am facing: How to compile a libtorrent(rasterbar) code ?

Does anyone know what caused this failure?