  The dominant mechanism to produce hadronic bound states with large transverse
momentum is fragmentation, that is the splitting of a high energy parton into a
hadronic state and other partons. We review the present schemes to calculate
the heavy quark fragmentation functions (FFs) and drive an exact analytical
expression of FF which includes most of the kinematical and dynamical
properties of the process. Using the perturbative QCD, we calculate the FF for
c-quark to split into S-wave D-meson to leading order in the QCD coupling
constant. Our result is compared with the current well-known phenomenological
models which are obtained through a global fit to e+e- data from SLAC SLC and
CERN LEP1 and we also compare the FF with experimental data form BELLE and
CLEO. Specically, we study the effect of outgoing meson mass on the pQCD FF.
Meson masses are responsible for the low-z threshold, where z is the scaled
energy variable.
