title: error: expected primary-expression before ')' token
body: <p>I'm trying displaying widget 'widg' in layer on MainWindow after pushing 'pushButton_2' but I'm receive this error: "expected primary-expression before ')' token"</p>
  
  <p>mainwindow.cpp</p>
  
  <pre><code>#include "mainwindow.h"
  #include "ui_mainwindow.h"
  #include "widg.h"
  #include "ui_widg.h"
  
  MainWindow::MainWindow(QWidget *parent) :
      QMainWindow(parent),
      ui(new Ui::MainWindow)
  {
      ui-&gt;setupUi(this);
  
      QObject::connect(ui-&gt;pushButton_2, SIGNAL(clicked()), SLOT(slotPush2()));
  }
  
  MainWindow::~MainWindow()
  {
      delete ui;
  }
  
  void MainWindow::slotPush2()
  {
      ui-&gt;verticalLayout_3-&gt;addWidget(widg);
  }
  </code></pre>
  
  <p>mainwindow.h</p>
  
  <pre><code>#ifndef MAINWINDOW_H
  #define MAINWINDOW_H
  
  #include &lt;QMainWindow&gt;
  
  namespace Ui {
  class MainWindow;
  }
  
  class MainWindow : public QMainWindow
  {
      Q_OBJECT
  
  public:
      explicit MainWindow(QWidget *parent = 0);
      ~MainWindow();
  
  private:
      Ui::MainWindow *ui;
  
  private slots:
      void slotPush2();
  };
  
  
  #endif // MAINWINDOW_H
  </code></pre>
  
  <p>widg.h</p>
  
  <pre><code>#ifndef WIDG_H
  #define WIDG_H
  
  #include &lt;QWidget&gt;
  
  namespace Ui {
  class widg;
  }
  
  class widg : public QWidget
  {
      Q_OBJECT
  
  public:
      explicit widg(QWidget *parent = 0);
      ~widg();
  
  private:
      Ui::widg *ui;
  };
  
  #endif // WIDG_H
  </code></pre>
  
  <p>widg.cpp</p>
  
  <pre><code>#include "widg.h"
  #include "ui_widg.h"
  
  widg::widg(QWidget *parent) :
      QWidget(parent),
      ui(new Ui::widg)
  {
      ui-&gt;setupUi(this);
  }
  
  widg::~widg()
  {
      delete ui;
  }
  </code></pre>
  
  <p>Please, help me, what is my mistake?</p>