  The CoRoT mission has provided thousands of red-giant light curves. The
analysis of their solar-like oscillations allows us to characterize their
stellar properties. Up to now, the global seismic parameters of the pressure
modes remain unable to distinguish red-clump giants from members of the
red-giant branch. As recently done with Kepler red giants, we intend to analyze
and use the so-called mixed modes to determine the evolutionary status of the
red giants observed with CoRoT. We also aim at deriving different seismic
characteristics depending on evolution. The complete identification of the
pressure eigenmodes provided by the red-giant universal oscillation pattern
allows us to aim at the mixed modes surrounding the l=1 expected
eigenfrequencies. A dedicated method based on the envelope autocorrelation
function is proposed to analyze their period separation. We have identified the
mixed-mode signature separation thanks to their pattern compatible with the
asymptotic law of gravity modes. We have shown that, independent of any
modelling, the g-mode spacings help to distinguish the evolutionary status of a
red-giant star. We then report different seismic and fundamental properties of
the stars, depending on their evolutionary status. In particular, we show that
high-mass stars of the secondary clump present very specific seismic
properties. We emphasize that stars belonging to the clump were affected by
significant mass loss. We also note significant population and/or evolution
differences in the different fields observed by CoRoT.
