  An explicit upper bound is derived for the modulus of divided difference for
a smooth(not necessarily analytic) function defined on a smooth Jordan arc (or
a smooth Jordan curve) in the complex plane. As an immediate application, an
error estimate for complex polynomial interpolation on a Jordan arc (or a
Jordan curve) is given, which extends the well-known error estimate for
polynomial interpolation on the unit interval. Moreover, this upper bound is
independent of the parametrization of the curve.
