Сериализация

stream >> size >> current;

//-----------------------------------------------------
void graficData::saveToFile(QString filename){
        QFile file(filename);
        QDataStream stream( &file );
 
        file.open( QIODevice::WriteOnly );
        stream << size << current;
        for(int i = 0; i < current; ++i)
            stream << point_x[i] << point_y[i];
        file.close();
}
//-----------------------------------------------------
void graficData::loadFromFile(QString filename){
    QFile file(filename);
    QDataStream stream( &file );
 
    file.open( QIODevice::ReadOnly );
    stream >> size >> current;
    for(int i = 0; i < current; ++i)
        stream >> point_x[i] >> point_y[i];
    file.close();
}

stream >> size >> current;

void DrawGraph::on_loadBtn_clicked()
{
    QString fileName = QFileDialog::getOpenFileName(this,
            tr("Choose filename"), "", tr("graphic files (*.grf)"));
    points->loadFromFile(fileName);
    QGraphicsScene *scene = new QGraphicsScene(ui->graphicsView);
    QPen pen(Qt::red, 3);
    points = new graficData(0);
    points->drawGraf(scene, pen);
    ui->graphicsView->setScene(scene);
}

this->size = size;

void graficData::loadFromFile(QString filename){
    QFile file(filename);
    QDataStream stream( &file );
    int size, current;
    file.open( QIODevice::ReadOnly );
    stream >> size;
    this->size = size;
    stream >> current;
    this->current = current;
    point_x = new double[size];
    point_y = new double[size];
    for(int i = 0; i < current; ++i)
        stream >> point_x[i] >> point_y[i];
    file.close();
}

graficData::graficData(int size)
{
    this->size = size;
    this->current = 0;
    this->point_x = new qreal[size];
    point_y = new qreal[size];
}

bool graficData::loadFromFile(QString filename)
{
    QFile file(filename);
 
    int size, current;
    if(!file.open( QIODevice::ReadOnly )) /* А если файла такого нет ? */ 
       return false;
 
    stream >> size;
    this->size = size;
    stream >> current;
    this->current = current;
    
    delete point_x;   // Память не резиновая не умеешь работать с ней используй QVector
    delete point_y;
 
    point_x = new double[size];
    point_y = new double[size];
 
    for(int i = 0; i < current; ++i)
        stream >> point_x[i] >> point_y[i]; /*  успешность чтения как бы тоже желательно проверять */
  
    return true;
}

graficData::graficData(int size)
   :size(size),
    current(0),
    point_x(new qreal[size]),
    point_y(new qreal[size])
{
   /* Используем список инициализации */
 
}

delete[] point_x; 
delete[] point_y;