Under Qt 5.3, the default button of a QButtonBox is Cancel and I want to set it to Ok but I can't find a way to achieve it. I've tried this :

QPushButton * b = ui->buttonBox->button(QDialogButtonBox::Ok);
b->setDefault(true);

but with no success, it throws :

/Users/thomas/Dev/Joker/app/Joker/RulerSpaceDialog.cpp:18:3: error: member access into incomplete type 'QPushButton'
        b->setDefault(true);
         ^
/Applications/Qt/5.3/clang_64/lib/QtWidgets.framework/Versions/5/Headers/qdialog.h:50:7: note: forward declaration of 'QPushButton'
class QPushButton;
      ^
1 error generated.

I also try by browsing the list but with no luck....

EDIT :

I added the include to get that code :

QPushButton * b = ui->buttonBox->button(QDialogButtonBox::Ok);
if(b)
{
    b->setDefault(true);
    qDebug() << b->text();
}

Which outputs Ok waits 2secs then highlight the Cancel button...

Make sure you set auto default false as well, use setAutoDefault(false) as well as setDefault(false).

Example code below.

#include <QtWidgets>

int main(int argc, char** argv)
{
  QApplication app(argc, argv);
  
  QDialogButtonBox* bb = new QDialogButtonBox(
    QDialogButtonBox::Ok | QDialogButtonBox::Cancel);

  QPushButton* okBtn = bb->button(QDialogButtonBox::Ok);
  okBtn->setAutoDefault(true);
  okBtn->setDefault(true);
  
  QPushButton* caBtn = bb->button(QDialogButtonBox::Cancel);
  caBtn->setAutoDefault(false);
  caBtn->setDefault(false);
  
  QDialog dlg;
  QVBoxLayout* dlgLayout = new QVBoxLayout();
  dlgLayout->addWidget(bb);
  dlg.setLayout(dlgLayout);
  dlg.show();
  return app.exec();
}

When I tested this on Windows, the OK button was the default button by default, but I could swap that to the cancel button by changing the calls to setAutoDefault and setDefault.