Segmentation error! Please help!!!

[phapha]

Hi all,
I'm a newbie in Qt; I've write a little program but I have segmentation error in run. I don't know how to fix it;
Below is my code:

main.cpp

#include <QApplication>
#include "FenetreAccueil.h"
 
int main(int argc,char* argv[])
{
    QApplication app(argc, argv);
    FenetreAccueil login;
    login.show();
    return app.exec();
}

#include <QApplication>
#include "FenetreAccueil.h"

int main(int argc,char* argv[])
{
    QApplication app(argc, argv);
    FenetreAccueil login;
    login.show();
    return app.exec();
}

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FenetreAccueil.h

#ifndef FENETREACCUEIL_H
#define FENETREACCUEIL_H
 
#include <QtGui>
//#include <QCoreApplication>
#include <QtSql>
#include "FenetrePrincipale.h"
 
 
class FenetreAccueil : public QWidget
{
    Q_OBJECT
 
    public:
        explicit FenetreAccueil(QWidget *parent = 0);
 
    public slots:
        void connectDB();
 
    private:
        QPushButton *m_connect;
        QPushButton *m_cancel;
       // QLineEdit *m_password;
        //QLineEdit *m_login;
        QLineEdit *m_addressBD;
        QLabel *m_label;
 
};
 
#endif // FENETREACCUEIL_H

#ifndef FENETREACCUEIL_H
#define FENETREACCUEIL_H

#include <QtGui>
//#include <QCoreApplication>
#include <QtSql>
#include "FenetrePrincipale.h"


class FenetreAccueil : public QWidget
{
    Q_OBJECT

    public:
        explicit FenetreAccueil(QWidget *parent = 0);

    public slots:
        void connectDB();

    private:
        QPushButton *m_connect;
        QPushButton *m_cancel;
       // QLineEdit *m_password;
        //QLineEdit *m_login;
        QLineEdit *m_addressBD;
        QLabel *m_label;

};

#endif // FENETREACCUEIL_H

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FenetreAccueil.cpp

#include "FenetreAccueil.h"
 
FenetreAccueil::FenetreAccueil(QWidget *parent) :
    QWidget(parent)
{
    //Creation du layout de formulaire et ses widgets
    QLineEdit *m_login=new QLineEdit;
    QLineEdit *m_password=new QLineEdit;
    m_password->setEchoMode(QLineEdit::Password);//affichage d'asterisques a la saisie
    QLineEdit *m_addressBD=new QLineEdit;//format adresse IP ou pas?
 
    QFormLayout *formAccueil=new  QFormLayout;
    formAccueil->addRow(tr("&Login"),m_login);
    formAccueil->addRow(tr("Password"),m_password);
    formAccueil->addRow(tr("mySQL server address"),m_addressBD);
 
    //Creation d'un layout horizontal pour les boutons
    m_connect=new QPushButton(tr("Connect"));
    m_cancel=new QPushButton(tr("Cancel"));
 
    QHBoxLayout *boutonLayout=new QHBoxLayout;
    boutonLayout->addWidget(m_connect);
    boutonLayout->addWidget(m_cancel);
 
 
    //Creation d'un layout pour le logo
    QLabel *logo=new QLabel(this);
    logo->setPixmap(QPixmap("images/grandlogo.png"));
 
    QHBoxLayout *logoLayout=new QHBoxLayout;
    logoLayout->addWidget(logo);
 
 
    //Creation d'un layout pour le message d'acceuil
    m_label = new QLabel(tr("Welcome in callTracker"),this);
 
    QHBoxLayout *labelLayout=new QHBoxLayout;
    labelLayout->addWidget(m_label);
 
    //Creation du layout principal de la fenetre
    QVBoxLayout *layoutPrincipal=new QVBoxLayout;
 
    //Ajout du layout d'accueil
    layoutPrincipal->addLayout(labelLayout);
 
    //Ajout du layout de formulaire
    layoutPrincipal->addLayout(formAccueil);
 
    //Ajout du layout des boutons
    layoutPrincipal->addLayout(boutonLayout);
 
    setLayout(layoutPrincipal);
    setWindowTitle(tr("Welcome"));
    setWindowFlags(Qt::Tool);//Pour empecher le changement de dimensions de la fenetre
    resize(300,350);
 
    //Generation des signaux et des slots
    connect(m_connect,SIGNAL(clicked()),this,SLOT(connectDB()));
    connect(m_cancel,SIGNAL(clicked()),this, SLOT(quit()));
}
 
void FenetreAccueil::connectDB()
{
    QString server;
   [B] server=m_addressBD->text();[/B] //HERE IS THE ERROR !!!!!!!!!!!!!!!
 
    if(server)
 
    QSqlDatabase db=QSqlDatabase::addDatabase("QMYSQL");
    db.setHostName(server);
    db.setDatabaseName("callTracker");
    db.setUserName("appClient");
    db.setPassword("Clown2neige");
    bool ok=db.open();
    //dataB.exec();
 
    //QApplication app2();
    if(ok)
    {
        FenetrePrincipale *fenP;
        fenP->show();
     }
    else
        QMessageBox::critical(this,"callTracker",tr("Connection to database failed"));
 
 
}

#include "FenetreAccueil.h"

FenetreAccueil::FenetreAccueil(QWidget *parent) :
    QWidget(parent)
{
    //Creation du layout de formulaire et ses widgets
    QLineEdit *m_login=new QLineEdit;
    QLineEdit *m_password=new QLineEdit;
    m_password->setEchoMode(QLineEdit::Password);//affichage d'asterisques a la saisie
    QLineEdit *m_addressBD=new QLineEdit;//format adresse IP ou pas?

    QFormLayout *formAccueil=new  QFormLayout;
    formAccueil->addRow(tr("&Login"),m_login);
    formAccueil->addRow(tr("Password"),m_password);
    formAccueil->addRow(tr("mySQL server address"),m_addressBD);

    //Creation d'un layout horizontal pour les boutons
    m_connect=new QPushButton(tr("Connect"));
    m_cancel=new QPushButton(tr("Cancel"));

    QHBoxLayout *boutonLayout=new QHBoxLayout;
    boutonLayout->addWidget(m_connect);
    boutonLayout->addWidget(m_cancel);


    //Creation d'un layout pour le logo
    QLabel *logo=new QLabel(this);
    logo->setPixmap(QPixmap("images/grandlogo.png"));

    QHBoxLayout *logoLayout=new QHBoxLayout;
    logoLayout->addWidget(logo);


    //Creation d'un layout pour le message d'acceuil
    m_label = new QLabel(tr("Welcome in callTracker"),this);

    QHBoxLayout *labelLayout=new QHBoxLayout;
    labelLayout->addWidget(m_label);

    //Creation du layout principal de la fenetre
    QVBoxLayout *layoutPrincipal=new QVBoxLayout;

    //Ajout du layout d'accueil
    layoutPrincipal->addLayout(labelLayout);

    //Ajout du layout de formulaire
    layoutPrincipal->addLayout(formAccueil);

    //Ajout du layout des boutons
    layoutPrincipal->addLayout(boutonLayout);

    setLayout(layoutPrincipal);
    setWindowTitle(tr("Welcome"));
    setWindowFlags(Qt::Tool);//Pour empecher le changement de dimensions de la fenetre
    resize(300,350);

    //Generation des signaux et des slots
    connect(m_connect,SIGNAL(clicked()),this,SLOT(connectDB()));
    connect(m_cancel,SIGNAL(clicked()),this, SLOT(quit()));
}

void FenetreAccueil::connectDB()
{
    QString server;
   [B] server=m_addressBD->text();[/B] //HERE IS THE ERROR !!!!!!!!!!!!!!!

    if(server)
    
    QSqlDatabase db=QSqlDatabase::addDatabase("QMYSQL");
    db.setHostName(server);
    db.setDatabaseName("callTracker");
    db.setUserName("appClient");
    db.setPassword("Clown2neige");
    bool ok=db.open();
    //dataB.exec();

    //QApplication app2();
    if(ok)
    {
        FenetrePrincipale *fenP;
        fenP->show();
     }
    else
        QMessageBox::critical(this,"callTracker",tr("Connection to database failed"));

    
}

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Thanks for your help.