occt-safe

name: occt-safe description: OCCT Handle<> null-check patterns. Use when writing kernel code to prevent crashes. license: MIT metadata: category: kernel priority: high

When to Use

• Writing any OCCT-touching code
• Debugging crashes in kernel
• Code review of kernel changes

CRITICAL: Always Null-Check Handle<>

OCCT Handle<> objects can be null. Dereferencing without check = crash.

Safe Patterns

Before accessing shape

Handle(TopoDS_Shape) shape = ...;
if (shape.IsNull()) {
    // Handle error
    return;
}
// Now safe to use

Before BRep operations

Handle(Geom_Surface) surface = BRep_Tool::Surface(face);
if (surface.IsNull()) {
    std::cerr << "No surface on face" << std::endl;
    return false;
}

Shape validity check

if (shape.IsNull()) return false;
BRepCheck_Analyzer analyzer(shape);
if (!analyzer.IsValid()) {
    // Shape is malformed
}

Builder result check

BRepPrimAPI_MakeBox mkBox(10, 10, 10);
if (!mkBox.IsDone()) {
    // Construction failed
    return;
}
TopoDS_Shape box = mkBox.Shape();

Common Crash Points

1. BRep_Tool::Surface(face) - face may have no surface
2. BRep_Tool::Curve(edge) - edge may be degenerate
3. TopoDS::Face(shape) - shape may not be a face
4. TopExp_Explorer iteration - shapes may be empty
5. BRepAlgoAPI_* results - Boolean ops can fail

ElementMap Interaction

const ElementMapEntry* entry = emap.find(topId);
if (!entry || entry->shape.IsNull()) {
    // Entry doesn't exist or shape was deleted
}