[Qt4-Win] problème avec QLineEdit

Bonsoir et joyeuse pâque à tous!

Bon je suis en train de réaliser un projet mais j'ai un soucis pour écupérer le texte saisie dans un QLineEdit.
Bon voici l'erreur :

C:\programmations\Calculs_Electro>make
mingw32-make -f Makefile.Release
mingw32-make[1]: Entering directory `C:/programmations/Calculs_Electro'
g++ -c -O2 -frtti -fexceptions -mthreads -Wall -DUNICODE -DQT_LARGEFILE_SUPPORT
-DQT_DLL -DQT_NO_DEBUG -DQT_GUI_LIB -DQT_CORE_LIB -DQT_THREAD_SUPPORT -I"d:\QT\i
nclude\QtCore" -I"d:\QT\include\QtCore" -I"d:\QT\include\QtGui" -I"d:\QT\include
\QtGui" -I"d:\QT\include" -I"." -I"d:\QT\include\ActiveQt" -I"release" -I"." -I"
d:\QT\mkspecs\win32-g++" -o release\intensite.o continu\intensite.cpp
continu\intensite.cpp: In constructor `Intensite::Intensite(QWidget*)':
continu\intensite.cpp:19: error: 'class QString' has no member named 'text'
continu\intensite.cpp:20: error: 'class QString' has no member named 'text'
continu\intensite.cpp: In member function `void Intensite::calculI()':
continu\intensite.cpp:50: error: invalid operands of types `const char[16]' and
`QString*' to binary `operator+'
mingw32-make[1]: *** [release\intensite.o] Error 1
mingw32-make[1]: Leaving directory `C:/programmations/Calculs_Electro'
mingw32-make: *** [release] Error 2

et voici mon code :

/*
intensite.h
-------------
*/
#ifndef H_INTENSITE_H
#define H_INTENSITE_H
 
#include <QWidget>
#include <QDialog>
#include <QPushButton>
#include <QLabel>
#include <QLineEdit>
#include <QString>
#include <QVBoxLayout>
#include <QHBoxLayout>
 
class QWidget;
class QDialog;
class QPushButton;
class QLabel;
class QLineEdit;
class QString;
class QVBoxLayout;
class QHBoxLayout;
 
class Intensite : public QDialog {
 
    public:
        Intensite(QWidget *parent=0);
        QString text () const;
    
    public slots:
        void calculI();
        
    private:
    
        QPushButton *m_calculer;
        QLabel *label_tension, *label_resistance; 
        QLabel *label_resultat;
        QString *string_tension, *string_resistance, *string_resultat;
        QLineEdit *m_tension, *m_resistance;
        QVBoxLayout *vLayout;
        QHBoxLayout *hLayoutTension, *hLayoutResistance;
 
};
 
#endif

/*
intensite.cpp
----------------
*/
 
#include "intensite.h"
 
Intensite::Intensite(QWidget *parent) : QDialog(parent)
{
    setFixedSize(500, 500);
    setWindowTitle(tr("Calculs élec - Intensité d'un courant continu"));
 
    label_tension = new QLabel("Tension : ");
    m_tension   = new QLineEdit;
/*
autre code de QLineEdit
....
*/
    m_calculer = new QPushButton(tr("Calculer"));
    connect(m_calculer, SIGNAL(clicked()), this, SLOT(calculI())));
    
    hLayoutTension = new QHBoxLayout;
    hLayoutTension->addWidget(label_tension);
    hLayoutTension->addWidget(m_tension);
    
    hLayoutResistance = new QHBoxLayout;
    hLayoutResistance->addWidget(label_resistance);
    hLayoutResistance->addWidget(m_resistance);
    
    vLayout = new QVBoxLayout;
    vLayout->addLayout(hLayoutTension);
    vLayout->addLayout(hLayoutResistance);
    vLayout->addWidget(m_calculer);
    
    setLayout(vLayout);
}
 
void Intensite::calculI()
{
    double tension    = string_tension->toDouble();
    double resistance = string_resistance->toDouble();
    double resultat   = tension/resistance;
    
    string_resultat   = new QString;
    string_resultat->setNum(resultat);
    
    label_resultat    = new QLabel(tr("I = U : R \nI = "+string_tension+" : "+string_resistance+"\nI = "+string_resultat));
    
    vLayout->addWidget(label_resultat);
    
    setLayout(vLayout);
}

Je ne vois pas pourquoi il me dis que text est faux.
Donc je vois encore moins comment récupérer le texte d'un QLineEdit.
J'ai été voir dans la doc avant http://doc.trolltech.com/4.3/qlineedit.html#text-prop

Voilà pouvez-vous m'aider?

Merci!