undefined reference to异常怎么解决

undefined reference to错误如何解决
想写一个在后台监视短信的exe程序，
MyStart.cpp

#include   <e32base.h>
#include   <e32std.h>
#include   <e32cons.h>                         //   Console
#include   "MyObserver.h "

_LIT(KTextConsoleTitle,   "Console ");
_LIT(KTextFailed,   "   failed,   leave   code   =   %d ");
_LIT(KTextPressAnyKey,   "   [press   any   key]\n ");

LOCAL_D   CConsoleBase*   console;     //   write   all   messages   to   this

LOCAL_C   void   DoStartL()
        {
        //   Create   active   scheduler   (to   run   active   objects)
        CActiveScheduler*   scheduler   =   new   (ELeave)   CActiveScheduler();
        CleanupStack::PushL(scheduler);
        CActiveScheduler::Install(scheduler);

        CMyObserver*   observer   =   CMyObserver::NewL(*console);
        observer-> Load();
        //CActiveScheduler::Start();
        //   Delete   active   scheduler
        CleanupStack::PopAndDestroy(scheduler);
        }

GLDEF_C   TInt   Start()
        {
        //   Create   cleanup   stack
        __UHEAP_MARK;
        CTrapCleanup*   cleanup   =   CTrapCleanup::New();

        //   Create   output   console
        TRAPD(createError,   console   =   Console::NewL(KTextConsoleTitle,   TSize(KConsFullScreen,KConsFullScreen)));
        if   (createError)
                return   createError;

        //   Run   application   code   inside   TRAP   harness,   wait   keypress   when   terminated
        TRAPD(mainError,   DoStartL());
        if   (mainError)
                console-> Printf(KTextFailed,   mainError);
        console-> Printf(KTextPressAnyKey);
        console-> Getch();
       
        delete   console;
        delete   cleanup;
        __UHEAP_MARKEND;
        return   KErrNone;
        }


//     Exported   Functions

#ifdef   __WINS__
EXPORT_C   TInt   WinsMain(TAny*   /*aParam*/)
        {
        return   Start();
        }
#else
GLDEF_C   TInt   E32Main()
        {
        return   Start();
        }
#endif

#ifdef   __WINS__
TInt   E32Dll(TDllReason   /*aReason*/)
        {