AcApDocumentIterator* pDociterator;
AcApDocument* pDoc;

pDociterator = acDocManager->newAcApDocumentIterator();

for (; !pDociterator->done(); pDociterator->step())
{
pDoc = pDociterator->document();

acdbSetDbmod(pDoc->database(),0); // 就是這句代碼起了決定性作用
acDocManager->closeDocument(pDoc);
}