After I build LAMMPS as a library, and the library has 3 callable
function, lammps_open, lammps_close, lammps_command. After the
application calls these three functions, can I access the atom
trajectory, and how could I get these data?
after you "close" I don't think you can do anything - LAMMPS will have
deleted all it's classes
your best bet is to tell LAMMPS (via lammps_command) to dump
stuff out in files. Or you could use fix print to print data about an
atom's trajectory ...