hi to all, i've centos 6.6 in VM and Qt 5.2. i am building a small project having this problem

Qt Code: 
  1. /opt/projects/Qt/find/spreadsheetmainwindow.cpp:52: error: undefined reference to `SpreadSheetMainWindow::loadFile(QString const&)'
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even i have declared in header file(spreadsheetmainwindow.h)
Qt Code: 
  1. void SpreadSheetMainWindow::open()
  2. {
  3.     if(okToContinue())
  4.     {
  5.         QString fileName = QFileDialog::getOpenFileName(this, "OPEN SP FILES", ".",
  6.                                                         "SpreadSheet Files (*.sp)");
  7.         if(!fileName.isEmpty())
  8.             loadFile(fileName);//here is error
  9.     }
  10. }
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and not only for this loadFile(filename) function but for most of functions declared in header file.
as in :-
Qt Code: 
  1. undefined reference to `SpreadSheetMainWindow::setFormula(int, int, QString const&)'
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header file is :-

Qt Code: 
  1. #ifndef SPREADSHEETMAINWINDOW_H
  2. #define SPREADSHEETMAINWINDOW_H
  3.  
  4. #include <QMainWindow>
  5. #include <QTableWidget>
  6. #include <QLabel>
  7. #include <QMessageBox>
  8. #include <QFileDialog>
  9. #include <QCloseEvent>
  10. #include <QClipboard>
  11. #include <QObject>
  12. #include <QLineEdit>
  13. #include <QDataStream>
  14. #include <QFile>
  15. #include <QTableWidgetSelectionRange>
  16.  
  17. #include "sortdialog.h"
  18. #include "gotocelldialog.h"
  19. #include "finddialog.h"
  20. #include "cell.h"
  21.  
  22. namespace Ui {
  23. class SpreadSheetMainWindow;
  24. }
  25.  
  26. class Cell;
  27. class SpreadsheetCompare;
  28. class gotoCellDialog;
  30.  
  31. class SpreadSheetMainWindow : public QMainWindow//, public QTableWidget
  32. {
  33.     Q_OBJECT
  34.  
  35. public:
  36.     bool autoRecalculate() const { return autoRecalc; }
  37.     QString currentLocation() const;
  38.     QString currentFormula() const;
  39.     QTableWidgetSelectionRange selectedRange() const;
  40.     void clear();
  41.     bool readFile(const QString &fileName);
  42.     bool writeFile(const QString &fileName);
  43.     void sort(const SpreadsheetCompare &compare);
  44.  
  45.  
  46. public:
  47.     explicit SpreadSheetMainWindow(QWidget *parent = 0);
  48.     ~SpreadSheetMainWindow();
  49.     void ConnectActions();
  50.  
  51. protected:
  52.     void closeEvent(QCloseEvent *event);
  53.  
  54. private slots:
  55.     void newFile();
  56.     void open();
  57.     bool save();
  58.     bool saveAs();
  59.     void find();
  60.     void goToCell();
  61.     void sort();
  62.     void about();
  63.     void openRecentFile();
  64.     void updateStatusBar();
  65.     void spreadsheetModified();
  66.  
  67. signals:
  68.  
  69.     void modified();
  70.  
  71. private slots:
  72.     void somethingChanged();
  73. public slots:
  74.     void cut();
  75.     void copy();
  76.     void paste();
  77.     void del();
  78.     void selectCurrentRow();
  79.     void selectCurrentColumn();
  80.     void recalculate();
  81.     void setAutoRecalculate(bool recalc);
  82.     void findNext(const QString &str, Qt::CaseSensitivity cs);
  83.     void findPrevious(const QString &str, Qt::CaseSensitivity cs);
  84.  
  85.  
  86. private:
  87.     enum { MagicNumber = 0x7F51C883, RowCount = 999, ColumnCount = 26 };
  88.  
  89.     Cell *cell(int row, int column) const;
  90.     QString text(int row, int column) const;
  91.     QString formula(int row, int column) const;
  92.     void setFormula(int row, int column, const QString &formula);
  93.  
  94.     bool autoRecalc;
  95.  
  96.     void configureStatusBar();
  97.  
  98. private:
  99.     Ui::SpreadSheetMainWindow *ui;
  100.     QLabel *labellocation;
  101.     QLabel *labelformula;
  102.     gotoCellDialog *dialog;
  103.  
  104. private:
  105.     void createContextMenu();
  106.     void readSettings();
  107.     void writeSettings();
  108.  
  109.     bool okToContinue();
  110.     bool loadFile(const QString &fileName);
  111.     bool saveFile(const QString &fileName);
  112.     void setCurrentFile(const QString &fileName);
  113.     void updateRecentFileActions();
  114.     QString strippedName(const QString &fullFileName);
  115.  
  116.   //  Spreadsheet *spreadsheet;
  117.     FindDialog *findDialog;
  118.     QLabel *locationLabel;
  119.     QLabel *formulaLabel;
  120.     QStringList recentFiles;
  121.     QString curFile;
  122.     enum { MaxRecentFiles = 5 };
  123.     QAction *recentFileActions[MaxRecentFiles];
  124.     QAction *separatorAction;
  125.     QTableWidget *tablewidget;
  126. };
  127.  
  128. class SpreadsheetCompare
  129. {
  130. public:
  131.     bool operator()(const QStringList &row1,
  132.                     const QStringList &row2) const;
  133.  
  134.     enum { KeyCount = 3 };
  135.     int keys[KeyCount];
  136.     bool ascending[KeyCount];
  137. };
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please suggest me how t recover this " undefined reference " problem.