仔细看下面解释：
int QMessageBox::warning ( QWidget * parent, const QString & caption, const QString & text, const QString & button0Text = QString::null, const QString & button1Text = QString::null, const QString & button2Text = QString::null, int defaultButtonNumber = 0, int escapeButtonNumber = -1 ) [static]
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
Displays a warning message box with a caption, a text, and 1, 2 or 3 buttons. Returns the number of the button that was clicked (0, 1, or 2).
button0Text is the text of the first button, and is optional. If button0Text is not supplied, "OK" (translated) will be used. button1Text is the text of the second button, and is optional, and button2Text is the text of the third button, and is optional. defaultButtonNumber (0, 1 or 2) is the index of the default button; pressing Return or Enter is the same as clicking the default button. It defaults to 0 (the first button). escapeButtonNumber is the index of the Escape button; pressing Escape is the same as clicking this button. It defaults to -1; supply 0, 1, or 2 to make pressing Escape equivalent to clicking the relevant button.
If parent is 0, the message box becomes an application-global modal dialog box. If parent is a widget, the message box becomes modal relative to parent.
Note: If you do not specify an Escape button then if the Escape button is pressed then -1 will be returned. It is suggested that you specify an Escape button to prevent this from happening.
