OdWriteEx sample contains creating a circle with hyperlink. Search DbFiller.cpp for "hyperlink".
Here is sample code for creating MTEXT with hyperlink in field. Code:
OdDbMTextPtr pMText = OdDbMText::createObject();
pMText->setDatabaseDefaults(pRecord->database());
pRecord->appendOdDbEntity(pMText);
/**********************************************************************/
/* Set some properties */
/**********************************************************************/
pMText->setLocation(point);
pMText->setTextHeight(0.2);
pMText->setAttachment(OdDbMText::kTopLeft);
pMText->setContents(OD_T("Sample Hyperlink"));
pMText->setWidth(w * 7.0 / 8.0);
pMText->setTextStyle(styleId);
OdDbFieldPtr pTextField3 = OdDbField::createObject();
OdDbFieldPtr pField3_1 = OdDbField::createObject();
OdDbObjectId textFldId3 = pMText->setField(OD_T("TEXT"), pTextField3);
OdDbObjectId fldId3_1 = pTextField3->setField(OD_T(""), pField3_1);
pField3_1->setEvaluationOption(OdDbField::kAutomatic);
OdString fc6(OD_T("\\AcVar \\href \"http://forum.opendesign.com/showthread.php?14172-How-do-I-add-a-hyperlink-to-an-MTEXT-entity##Open Design Alliance Forum > Teigha, C++ version#0\""));
pField3_1->setFieldCode(fc6);
OdDbEntityHyperlinkPEPtr hpe = pField3_1;
OdDbHyperlinkCollectionPtr urls = hpe->getHyperlinkCollection(pField3_1);
urls->addTail(L"http://forum.opendesign.com/showthread.php?14172-How-do-I-add-a-hyperlink-to-an-MTEXT-entity##ForumLink#0\"",
L"Open Design Alliance Forum > Teigha, C++ version");
hpe->setHyperlinkCollection(pField3_1, urls);
pTextField3->setEvaluationOption(OdDbField::kAutomatic);
OdString fc7(OD_T("HyperLink sample %<\\_FldIdx 0>%"));
pTextField3->setFieldCode(fc7, OdDbField::FieldCodeFlag(OdDbField::kTextField | OdDbField::kPreserveFields));
pField3_1->evaluate(OdDbField::kAutomatic);