How to get value from QComboBox

[talmage]

All this code is in MainWindow class. In the header I define modelCell as

class MainWindow : public QMainWindow
{
    Q_OBJECT
public:
    QSqlQueryModel *modelCell;

class MainWindow : public QMainWindow
{
    Q_OBJECT
public:
    QSqlQueryModel *modelCell;

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Then I create the pointer. I thought this would allow the pointer to be used in any of the functions of the mainwindow class.

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    QSqlQueryModel *modelCell = new QSqlQueryModel(this);

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    QSqlQueryModel *modelCell = new QSqlQueryModel(this);

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Here is the function I am trying to access the pointer. What am I not doing correctly?
I must be missing something in my fundamental knowledge.

void MainWindow::on_btnSaveConductivityTest_clicked()
{
QSqlRecord record = modelCell->record(ui->cmbCellList->currentIndex());
        QString lstr;
       lstr = record.value(0).toString();
        ui->lineEdit->setText(lstr);

void MainWindow::on_btnSaveConductivityTest_clicked()
{
QSqlRecord record = modelCell->record(ui->cmbCellList->currentIndex());
        QString lstr;
       lstr = record.value(0).toString();
        ui->lineEdit->setText(lstr);

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