From Forum Nokia Wiki

Supports the creation or replacement of a stream a dictionary store.

To prepare a stream for writing, use the RDictionaryWriteStream::AssignL() or RDictionaryWriteStream::AssignLC() functions, passing a reference to the dictionary store and the UID associated with the stream.

If no stream is associated with the UID, then a new stream is created. An association is made between the resulting stream ID and the UID.

If a stream is currently associated with the specified UID, then the existing stream is prepared for replacement.

TUid theuid;
CDictionaryStore* store;
...
RDictionaryWriteStream outstream;
outstream.AssignLC(*store,theuid);
TSomeData data;
...
outstream << data;
outstream.CommitL()
CleanupStack::PopAndDestroy(); // cleanup the write stream
...
store->CommitL(); // commit changes to the dictionary store