ftp = new QFtp(this)

error: undefined reference to `_imp___ZN4QFtpC1EP7QObject'

#-------------------------------------------------
#
# Project created by QtCreator 2009-12-05T14:43:13
#
#-------------------------------------------------

TARGET = part
TEMPLATE = app


SOURCES += main.cpp
        part.cpp

HEADERS  += part.h

FORMS    += part.ui

#include <QApplication>
#include <QFile>
#include <QtNetwork/QFtp>

int main(int argc, char *argv[])
{
    QApplication app(argc, argv, false);
    QFtp ftp;

    QObject::connect(&ftp, SIGNAL(done(bool)), &app, SLOT(quit()));

    QFile file("INSTALL");

    ftp.connectToHost("ftp.trolltech.com");
    ftp.login();
    ftp.cd("qt");
    ftp.get("INSTALL", &file);
    ftp.close();

    return app.exec();
}

error: undefined reference to `QFtp::QFtp(QObject*)'

QT += network

#include <QtNetwork/QFtp>

int main()
{
...
QFtp * ftp = new QFtp();
ftp->connectToHost("mon_host");
ftp->login("utilisateur","password");
...
}

error: undefined reference to `_imp___ZN4QFtp13connectToHostERK7QStringt'

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    AdressBook w;
    w.show();
    return a.exec();
}