Libopencad is a library written in C++11, which provides a way to
read/write CAD  (DWG/DXF/DXFB) files. It was designed to have a
uniformal API to work with any CAD files.

It has a base class - CADFile.

Inheriting this class it's possible to create a driver for any CAD
format, all you need to do - is to overwrite interface functions
like GetGeometry(index), and others.

Now it has an implementation for DWG2000 (R15), but only for read.

Library comes with cadinfo utility, which prints out everything
library can get from file - header variables, CAD custom classes,
presented layers and geometries with their attributes.

WWW: https://trac.osgeo.org/gdal/wiki/DWG_driver