Cannot call function without object

[Salazaar]

Hi. I've got a problem. I have public member function called clear() which looks like this:

void MainWindow::clear()
            {
              tableWidget->clear();
              tableWidget_2->clear();
              tableWidget_3->clear();
              tableWidget_4->clear();
              tableWidget_5->clear();
              tableWidget_6->clear();
              tableWidget_7->clear(); 
             }

void MainWindow::clear()
            {
              tableWidget->clear();
              tableWidget_2->clear();
              tableWidget_3->clear();
              tableWidget_4->clear();
              tableWidget_5->clear();
              tableWidget_6->clear();
              tableWidget_7->clear(); 
             }

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and when I call it in another member function

MainWindow::clear()

MainWindow::clear()

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There appear error that I can't call member function MainWindow::clear() without object. What's the problem about? Regards