how to use arguments in Qt?

[stampede]

For example, add a second parameter in VerticalBox constructor:

VerticalBox( const QString& fileName = QString(), QWidget * parent = NULL )

VerticalBox( const QString& fileName = QString(), QWidget * parent = NULL )

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And use it to setup lineEdit in constructor:

VerticalBox::VerticalBox(const QString& fileName,QWidget *parent) : QWidget(parent)
{
  QVBoxLayout *vbox = new QVBoxLayout(this);
    QHBoxLayout *contentBox = new QHBoxLayout();
    QHBoxLayout *buttonBox = new QHBoxLayout();
 
//HBox contentBox containing the QLabel and QLineEdit:
  QLabel *name = new QLabel("Name: ", this);
  QLineEdit *name_in = new QLineEdit(this);
  name_in->setText(fileName);
  contentBox->addWidget(name);
  contentBox->addWidget(name_in);
...

VerticalBox::VerticalBox(const QString& fileName,QWidget *parent) : QWidget(parent)
{
  QVBoxLayout *vbox = new QVBoxLayout(this);
    QHBoxLayout *contentBox = new QHBoxLayout();
    QHBoxLayout *buttonBox = new QHBoxLayout();
 
//HBox contentBox containing the QLabel and QLineEdit:
  QLabel *name = new QLabel("Name: ", this);
  QLineEdit *name_in = new QLineEdit(this);
  name_in->setText(fileName);
  contentBox->addWidget(name);
  contentBox->addWidget(name_in);
...

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In order to pass the "fileName" argument you can use argv array:

...
QApplication app(argc, argv);
const QString toPass = argc > 1 ? QString(argv[1]) : QString();
VerticalBox window( toPass );

...
QApplication app(argc, argv);
const QString toPass = argc > 1 ? QString(argv[1]) : QString();
VerticalBox window( toPass );

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argv[0] is usually name of the program, argv[1], argv[2], ... are parameters passed.

You can also use QCoreApplication::arguments()