ObjectARX

ObjectARX is Autodesk's native application programming interface for AutoCAD, designed to let developers create plug-ins in C++ that run inside the AutoCAD process. It provides a framework for extending AutoCAD with custom commands, entities, data structures, and user interfaces, enabling performance-sensitive and tightly integrated automation. The ObjectARX SDK ships with libraries, headers, and sample code that developers compile into dynamic-link libraries (DLLs) and load into AutoCAD.

The API exposes a set of classes and services that interface with AutoCAD's internal database and graphics pipeline. Developers write ARX applications as DLLs that implement an initialization entry point and register new commands and objects. Typical extensions include custom commands, new entity types, reactors for event handling, and tool palettes or menus that integrate with the AutoCAD UI. The runtime executes the code within AutoCAD's process, providing direct access to the drawing database and geometric primitives.

Development workflow generally involves selecting the ObjectARX SDK version that matches the AutoCAD release, configuring a C++ project to link against the corresponding AutoCAD libraries, and building a DLL that exports an initialization function. The resulting ARX file is loaded into AutoCAD via commands such as netload or startup loading. Because ObjectARX is version-specific, plugins must be rebuilt for each major AutoCAD release.

ObjectARX plugins run only in AutoCAD (not in AutoCAD LT) and require matching Autodesk binaries to ensure compatibility. Although ObjectARX offers low-level access and high performance, many developers also use the AutoCAD .NET API for managed-code variants, or newer JavaScript-based APIs for modern automation tasks.

ObjectARX remains in use for legacy plugins and for tasks requiring native C++ access. See also: AutoCAD API, ARX, AutoCAD .NET API.