extra line when adding QToolBar into QMainWindow

Hi,

How can I avoid this line when adding QToolBar into mainwindow?
seems that there contains 2 tool bar?

Code:

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QToolBar* toolBar = new QToolBar(this);
   toolBar->setGeometry(0,0,200,20);
   this->addToolBar(toolBar);

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Attachment 9375

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Added after 1 31 minutes:

It seems that when one QMainWindow is created,
there is already one default ToolBar inside of it.

Quote:

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<QToolBar*> bars = this->findChildren<QToolBar*>();

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I get one tool bar element without calling addToolBar function...
But somehow I dont find similar functions like QMainWindow::menuBar() or QMainWindow::statusBar()...