如何从AcDb2dPolyline对象中获取AcGeCurve3d对象？

#include "StdAfx.h"
Acad::ErrorStatus Function(const AcDbEntity *& pEnt)
{
    acutPrintf(_T("\nCatch all for AcDbEntity types called. The entity is a %s"), pEnt->isA()->name());
    return Acad::eNotImplementedYet;
}
Acad::ErrorStatus Function(const AcDbLine *& pEnt)
{
    acutPrintf(_T("\nAcDbLine function called."));
    return eOk;
}
Acad::ErrorStatus Function(const AcDbCircle *& pEnt)
{
    acutPrintf(_T("\nAcDbCircle function called."));
    return eOk;
}
/*
 * The purpose of the function is to take an entity
 * derived from AcDbEntity, determine its type and
 * call the correct Function above.
 * kind of like a traffic cop, directing traffic.
 * Probably not the best function name in the world, but...
*/
Acad::ErrorStatus FunctionRouter(const AcDbEntity *& pEnt)
{
    if(pEnt->isKindOf(AcDbLine::desc()))
        return Function((const AcDbLine *&) pEnt);
    else if(pEnt->isKindOf(AcDbCircle::desc()))
        return Function((const AcDbCircle *&) pEnt);
    else if(pEnt->isKindOf(AcDbEntity::desc()))
        return Function((const AcDbEntity *&) pEnt);
    return eWrongObjectType;
}
void TestFunctionRouter(void)
{
    AcDbDatabase * pDb = acdbHostApplicationServices()->workingDatabase();
    AcDbBlockTableRecord * pRec;
    if(acdbOpenAcDbObject((AcDbObject *&) pRec, pDb->currentSpaceId(), AcDb::kForRead) == Acad::eOk) {
        AcDbBlockTableRecordIterator * pIter = NULL;
        if(pRec->newIterator(pIter) == Acad::eOk) {
            for(pIter->start(); !pIter->done(); pIter->step()) {
                AcDbEntity * pEnt = NULL;
                if(pIter->getEntity(pEnt, AcDb::kForRead) == Acad::eOk) {
                    Acad::ErrorStatus es;
                    // look ma', no ugly if/else if/else if/else junk in my routine                                        
                    es = FunctionRouter((const AcDbEntity *&)pEnt);
                    pEnt->close();
                }
            }
            delete pIter;
        }
        pRec->close();
    }        
}