invalid use of incomplete type/ foward declaration of

Question

I've been looking for info about this problem .. but none of the solutions I've found have helped me, I really hope that you can helpme

• maintabholder.h:

  #ifndef MAINTABHOLDER_H
  #define MAINTABHOLDER_H
  
  #include <QMainWindow>
  
  namespace Ui {
  class MainTabHolder;
  }
  
  class MainTabHolder : public QMainWindow
  {
      Q_OBJECT
  
  public:
      explicit MainTabHolder(QWidget *parent = 0);
      ~MainTabHolder();
  
  private:
      Ui::MainTabHolder *ui;
  };
  #endif // MAINTABHOLDER_H
  

• maintabholder.cpp:

  #include "maintabholder.h"
  #include "ui_maintabholder.h"
  
  MainTabHolder::MainTabHolder(QWidget *parent) :
      QMainWindow(parent),
      ui(new Ui::MainTabHolder)
  {
      ui->setupUi(this);
  }
  
  MainTabHolder::~MainTabHolder()
  {
      delete ui;
  }
  

• main.cpp:

  #include "maintabholder.h"
  #include <QApplication>
  
  int main(int argc, char *argv[])
  {
      QApplication a(argc, argv);
      MainTabHolder w;
      w.show();
      return a.exec();
  }
  

• ui_maintabholder.h #ifndef UI_MAINTABHOLDER_H #define UI_MAINTABHOLDER_H

  #include <QtCore/QVariant>
  #include <QtWebKitWidgets/QWebView>
  #include <QtWidgets/QAction>
  #include <QtWidgets/QApplication>
  #include <QtWidgets/QButtonGroup>
  #include <QtWidgets/QHBoxLayout>
  #include <QtWidgets/QHeaderView>
  #include <QtWidgets/QPushButton>
  #include <QtWidgets/QSpacerItem>
  #include <QtWidgets/QTabWidget>
  #include <QtWidgets/QVBoxLayout>
  #include <QtWidgets/QWidget>
  
  QT_BEGIN_NAMESPACE
  
  class Ui_Form
  {
  public:
      QHBoxLayout *horizontalLayout;
      QTabWidget *tabWidget;
      QWidget *comicViewer;
      QWidget *comicSearcher;
      QVBoxLayout *verticalLayout;
      QHBoxLayout *horizontalLayout_2;
      QPushButton *pushButton;
      QSpacerItem *horizontalSpacer;
      QPushButton *pushButton_2;
      QWebView *webView;
  
      void setupUi(QWidget *Form)
      {
          if (Form->objectName().isEmpty())
              Form->setObjectName(QStringLiteral("Form"));
          Form->resize(531, 308);
          horizontalLayout = new QHBoxLayout(Form);
          horizontalLayout->setObjectName(QStringLiteral("horizontalLayout"));
          tabWidget = new QTabWidget(Form);
          tabWidget->setObjectName(QStringLiteral("tabWidget"));
                  comicViewer = new QWidget();
          comicViewer->setObjectName(QStringLiteral("comicViewer"));
          comicViewer->setCursor(QCursor(Qt::ArrowCursor));
          tabWidget->addTab(comicViewer, QString());
          comicSearcher = new QWidget();
          comicSearcher->setObjectName(QStringLiteral("comicSearcher"));
          verticalLayout = new QVBoxLayout(comicSearcher);
          verticalLayout->setObjectName(QStringLiteral("verticalLayout"));
          horizontalLayout_2 = new QHBoxLayout();
          horizontalLayout_2->setObjectName(QStringLiteral("horizontalLayout_2"));
          pushButton = new QPushButton(comicSearcher);
          pushButton->setObjectName(QStringLiteral("pushButton"));
  
          horizontalLayout_2->addWidget(pushButton);
  
          horizontalSpacer = new QSpacerItem(40, 20, QSizePolicy::Expanding, QSizePolicy::Minimum);
  
          horizontalLayout_2->addItem(horizontalSpacer);
  
          pushButton_2 = new QPushButton(comicSearcher);
          pushButton_2->setObjectName(QStringLiteral("pushButton_2"));
          pushButton_2->setEnabled(false);
  
          horizontalLayout_2->addWidget(pushButton_2);
  
  
          verticalLayout->addLayout(horizontalLayout_2);
  
          webView = new QWebView(comicSearcher);
          webView->setObjectName(QStringLiteral("webView"));
          webView->setUrl(QUrl(QStringLiteral("about:blank")));
  
          verticalLayout->addWidget(webView);
  
          tabWidget->addTab(comicSearcher, QString());
  
          horizontalLayout->addWidget(tabWidget);
  
  
          retranslateUi(Form);
  
          tabWidget->setCurrentIndex(1);
  
  
          QMetaObject::connectSlotsByName(Form);
      } // setupUi
  
      void retranslateUi(QWidget *Form)
      {
          Form->setWindowTitle(QApplication::translate("Form", "Form", 0));
          tabWidget->setTabText(tabWidget->indexOf(comicViewer), QApplication::translate("Form", "Comic Viewer", 0));
          pushButton->setText(QApplication::translate("Form", "Go to SubManga", 0));
          pushButton_2->setText(QApplication::translate("Form", "Download Comic", 0));
          tabWidget->setTabText(tabWidget->indexOf(comicSearcher), QApplication::translate("Form", "Search For Comics", 0));
      } // retranslateUi
  
  };
  
  namespace Ui {
      class Form: public Ui_Form {};
  } // namespace Ui
  
  QT_END_NAMESPACE
  
  #endif // UI_MAINTABHOLDER_H
  

the compiler errors are:

    [...]\maintabholder.cpp: In constructor 'MainTabHolder::MainTabHolder(QWidget*)':
    [...]\maintabholder.cpp:6:16: error: invalid use of incomplete type 'class Ui::MainTabHolder'
    In file included from [...]\maintabholder.cpp:1:0:
    [...]\maintabholder.h:7:7: error: forward declaration of 'class Ui::MainTabHolder'
    [...]\maintabholder.cpp:8:7: error: invalid use of incomplete type 'class Ui::MainTabHolder'
    In file included from [...]\maintabholder.cpp:1:0:
    [...]\maintabholder.h:7:7: error: forward declaration of 'class Ui::MainTabHolder'
    [...]\maintabholder.cpp: In destructor 'virtual MainTabHolder::~MainTabHolder()':
    [...]\maintabholder.cpp:13:12: warning: possible problem detected in invocation of delete operator: [enabled by default]
    [...]\maintabholder.cpp:13:12: warning: invalid use of incomplete type 'class Ui::MainTabHolder' [enabled by default]
    In file included from [...]\maintabholder.cpp:1:0:
    [...]\maintabholder.h:7:7: warning: forward declaration of 'class Ui::MainTabHolder' [enabled by default]
    [...]\maintabholder.cpp:13:12: note: neither the destructor nor the class-specific operator delete will be called, even if they are declared when the class is defined

Can you give a help with this? I would appreciate it...

Answer 1

You included the ui define head in your .cpp file, and defined a private member "Ui::MainTabHolder *ui;" in your .h file, so you need to add a forward declaration in your .h file(maintabholder.h:) before your class defination:

class Ui_MainTabHolder;

here Ui_MainTabHolder is your Ui class name, check your own project for correct one.

Answer 2

You are using a file generated by uic from Qt; you should verify that this tool successfully generate the file, by for example checking the build output and the file itself. Also, check that it is in the *.pro file (ie, that maintabholder.h is marked to be processed by uic).

I personnally advise to use the multiple inheritance method for ui :

// in maintabholder.h
// ...
#include "ui_maintabholder.h"

class MainTabHolder : public QMainWindow, public Ui::MainTabHolder
{
    // ...
};

Simpler to use, and if you have a problem with the ui_*.h file the error is more explicit.

You should post ui_maintabholder.h.