Object Filing

Object filing refers to the conversion process between an object's state and a single sequence of data, for purposes such as storing it on disk, copying it, or recording its state for an undo operation. Filing out is sometimes called serializing. Filing an object in is the process of turning a sequence of data back into an object, sometimes called deserializing.

Filing is used in several contexts in AutoCAD:

• Writing and reading DWG files (uses DWG format)
• Writing and reading DXF files (uses DXF format)
• Communicating among AutoCAD, AutoLISP, and ObjectARX (uses DXF format)
• Undo recording and restoring (uses DWG format)
• Copying operations such as INSERT, XREF, and COPY (uses DWG format)
• Paging (uses DWG format)

AcDbObject has two member functions for filing out: dwgOut() and dxfOut(), and two member functions for filing in: dwgIn() and dxfIn(). These member functions are primarily called by AutoCAD; object filing is almost never explicitly controlled by applications that use the database. However, if your application implements new database object classes, you'll need a more in-depth understanding of object filing. See Deriving from AcDbObject.

The dwg- and dxf- prefixes indicate two fundamentally different data formats, the first typically used in writing to and from DWG files, and the second primarily for DXF files and AutoLISP entget, entmake, and entmod functions. The primary difference between the two formats is that for DWG filers (an object that writes data to a file), the data is not explicitly tagged. The DXF filers, in contrast, associate a data group code with every element of data in a published data format (see Deriving from AcDbObject).