Could not get focus on input widgets in mdisubwindow

Friends please help me if possible...
my application having a mdisubwindow, mainwindow and mdi area.. i set mdi area as central widget of mainwindow...added mdisubwindow to mdi... but itried to launch application using the following code ... but no input widget getting focus even.....if i shown any dialog or Qwidget before showing that mdisubwindow... everything works fine

Code:

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int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    mainWindow w;
    w.show();
 
    masterMenu *c=new masterMenu;
    c->show();
 
    return a.exec();
}

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