objectarx-cpp-development

ObjectARX C++ Development

Guide for writing correct C++ ObjectARX code using the oarx-docs MCP server.

Critical Rule

ALWAYS call lookup_class before using any ObjectARX C++ class or function. Never guess method signatures, parameter types, or return values. The ObjectARX API has 40,000+ documented items — look them up.

Before Writing Code

1. Look up every ObjectARX class you plan to use:

   lookup_class("AcDbLine", guide="arxref")
   

2. Check the developer guide for the pattern you need:

   search_docs("creating custom entities", guide="arxdev")
   

3. If unsure about class hierarchy, look up the base class first:

   lookup_class("AcDbEntity", guide="arxref")
   lookup_class("AcDbObject", guide="arxref")
   

Required Patterns

Open/Close Protocol

Every database object must be opened before access and closed after:

// PREFERRED: Smart pointer (RAII) — AcDbObjectPointer or AcDbSmartObjectPointer
AcDbObjectPointer<AcDbLine> pLine(lineId, AcDb::kForRead);
if (pLine.openStatus() != Acad::eOk) { /* handle error */ }
// pLine auto-closes on scope exit
// AcDbSmartObjectPointer<T> is similar but uses reference counting

// ALTERNATIVE: Manual open/close
AcDbLine* pLine = nullptr;
Acad::ErrorStatus es = acdbOpenObject(pLine, lineId, AcDb::kForRead);
if (es != Acad::eOk) { /* handle error */ }
// ... use pLine ...
pLine->close();

Error Status Checking

Always check Acad::ErrorStatus:

Acad::ErrorStatus es = pEntity->transformBy(xform);
if (es != Acad::eOk) {
    acutPrintf(_T("\nError: %s"), acadErrorStatusText(es));
    return es;
}

Object ID — Never Raw Pointers Across Boundaries

// WRONG: storing raw pointer
AcDbLine* pLine = ...; // pointer invalid after close!

// RIGHT: store ObjectId, reopen when needed
AcDbObjectId lineId = pLine->objectId();
pLine->close();
// later...
AcDbObjectPointer<AcDbLine> pLine2(lineId, AcDb::kForWrite);

Adding Entities to Model Space