Context for reading and writing streams: SetContext, GetContext

The TContext argument is used in the case where multiple references to the same object are flattened and packed together on the same stream. The TContext is basically a dynamic dictionary built during the flattening process to assign references to repeated object instances from a set of objects to be saved. If you only want to save a single instance, then the TContext can be generated automatically by the system.

If you want to save multiple instances (which might point to overlapping instances), you need to provide a TContext. The code sample below shows both single and multiple instance flattening techniques:

  // Flatten a single instance.
  TPersistentClassA* a = new TPersistentClassA('a', 5);
  TContiguousMemoryStream aStream(new char[100], 100);
  Flatten(a,aStream);
  
  // FlattenPointer two instances with shared parts
  TPersistentClassD* d = new TPersistentClassD("me", "cguy", "bguy", a);
  TMemory aStream(new char[100], 100);
  TContext aContext;
  if (!aStream>GetContext())
      aStream>SetContext(&aContext);
  aStream.FlattenPointer(d);
  aStream.FlattenPointer(a);
  if (aStream>GetContext() == &aContext)
      aStream>SetContext(NIL);