  The homogeneous spectroscopic determination of the stellar parameters is a
mandatory step for transit detections from space. Knowledge of which population
the planet hosting stars belong to places constraints on the formation and
evolution of exoplanetary systems. We used the FLAMES/GIRAFFE multi-fiber
instrument at ESO to spectroscopically observe samples of stars in three
CoRoT/Exoplanet fields, namely the LRa01, LRc01, and SRc01 fields, and
characterize their stellar populations. We present accurate atmospheric
parameters, Teff, logg, [M/H], and [$\alpha$/Fe]\ derived for 1227 stars in
these fields using the \matisse algorithm. The latter is based on the spectral
synthesis methodology and automatically provides stellar parameters for large
samples of observed spectra. We trained and applied this algorithm to \flames
observations covering the Mg \textsc{i} b spectral range. It was calibrated on
reference stars and tested on spectroscopic samples from other studies in the
literature. The barycentric radial velocities and an estimate of the Vsini
values were measured using cross-correlation techniques. We corrected our
samples in the LRc01 and LRa01 CoRoT fields for selection effects to
characterize their FGK dwarf stars population, and compiled the first unbiased
reference sample for the in-depth study of planet metallicity relationship in
these CoRoT fields. We conclude that the FGK dwarf population in these fields
mainly exhibit solar metallicity. We show that for transiting planet finding
missions, the probability of finding planets as a function of metallicity could
explain the number of planets found in the LRa01 and LRc01 CoRoT fields. This
study demonstrates the potential of multi-fiber observations combined with an
automated classifier such as MATISSE for massive spectral classification.
