AcDbArc(
    const AcGePoint3d& center, 
    double radius, 
    double startAngle, 
    double endAngle
);

Parameters	Description
const AcGePoint3d& center	Input center point of the arc
double radius	Input radius of the arc
double startAngle	Input starting angle of the arc
double endAngle	Input ending angle of the arc

AcDbArc(
    const AcGePoint3d& center, 
    const AcGeVector3d& normal, 
    double radius, 
    double startAngle, 
    double endAngle
);

Parameters	Description
const AcGePoint3d& center	Input center point of the arc
const AcGeVector3d& normal	Input normal vector of the plane containing the arc
double radius	Input radius of the arc
double startAngle	Input starting angle of the arc
double endAngle	Input ending angle of the arc

#define PI 3.1415926535897932384626433832795L

//建立圓弧
AcGePoint3d ptSart(0,0,0);
//輸入的角度是弧度

AcDbArc *pArc= new AcDbArc(ptSart,200,0 , 90* PI / 180.0);

if (pArc == NULL)
       return;

  //將實體新增到模型空間是固定的程式碼，
AcDbDatabase* pDb = NULL;
pDb = acdbHostApplicationServices()->workingDatabase();
if (pDb == NULL)
return ;


AcDbBlockTable * pBlkTable ; 
if(pDb->getBlockTable(pBlkTable , AcDb::kForRead) != Acad::eOk ) 
return ;


AcDbBlockTableRecord * pRec ;
if(pBlkTable->getAt(ACDB_MODEL_SPACE , pRec , AcDb::kForWrite) != Acad::eOk) 
return ;
pBlkTable->close();


AcDbObjectId objId = AcDbObjectId::kNull;


if(pRec->appendAcDbEntity(objId, pArc) != Acad::eOk)  //將線新增到dwg中
return ;


pArc->close() ;
pRec->close() ;