I'm working on my multi-threaded project and got this error on build. I did not require any initialization with my threads and I just made an instance of the thread in the private section of my QMainWindow.
error: field 'capturingThread' has incomplete type
error: field 'computingThread' has incomplete type
The following code is my main window and the error points to the private section here.
Qt Code: 
  1. #ifndef GENIUS_H
  2. #define GENIUS_H
  3.  
  4. #include <QMainWindow>
  5. #include "ui_genius.h"
  6.  
  7. class CapturingThread;
  8. class ComputingThread;
  9.  
  10. class GeniusMain : public QMainWindow, private Ui::genius
  11. {
  12.     Q_OBJECT
  13.  
  14.     public:
  15.        GeniusMain(QMainWindow *parent);
  16.  
  17.     protected:
  18.        void closeEvent (QCloseEvent *event);
  19.  
  20.     private slots:
  21.        void standbyThreads();
  22.        void startTransmission();
  23.        void haltThreads();
  24.        void printFPS();
  25.        void printDistance();
  26.        void printTeam();
  27.        void printOpp();
  28.  
  29.     private:
  30.        CapturingThread capturingThread;
  31.        ComputingThread computingThread;
  32. };
  33.  
  34. #endif
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Here are the header files for my threads capturingThread and computingThread.
Qt Code: 
  1. #ifndef CAPTURINGTHREAD_H
  2. #define CAPTURINGTHREAD_H
  3.  
  4. #include <QThread>
  5.  
  6. class ImageBuffer;
  7.  
  8. class CapturingThread : public QThread 
  9. {
  10.     public:
  11.        CapturingThread();
  12.        ~CapturingThread();
  13.  
  14.        void haltCapture();
  15.  
  16.     protected:
  17.        void run();
  18.  
  19.     private:
  20.        volatile bool halt;
  21.        ImageBuffer* imageBuffer;
  22. };
  23.  
  24. #endif
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Qt Code: 
  1. #ifndef COMPUTINGTHREAD_H
  2. #define COMPUTINGTHREAD_H
  3.  
  4. #include <QThread>
  5.  
  6. class ImageBuffer;
  7.  
  8. class ComputingThread : public QThread
  9. {
  10.     public:
  11.        ComputingThread();
  12.        ~ComputingThread();
  13.  
  14.        void haltComputing();
  15.        void startTransmitting();
  16.        void stopTransmitting();
  17.  
  18.     protected:
  19.        void run();
  20.  
  21.     private:
  22.        volatile bool halt;
  23.        volatile bool transmit;
  24.        ImageBuffer* imageBuffer;
  25. };
  26.  
  27. #endif
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What could be the source of the build error?