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Earlier versions of the library included an Xbase specific functin called "Real Delete"
The analysis is as follows:
Updates to xbdbf.h and xbdbf.cpp
#ifdef XB_REAL_DELETE
...
#endif
Functions included:
RealDeleteOn() Turns on RealDelete
RealDeleteOff() Turns off RealDelete
GetRealDelete() Returns the status of RealDelete
Narrative:
This should be done before creating a database with xbDbf::CreateDatabase() and
thereafter before opening a database with xbDbfCreateDatabase()
You can not turn on real deletes once a database has been created and records added
In the Table header
bytes 12-15 - FirstFreeRec;
bytes 16-19 - RealNumRecs
Updates to the following methods:
WriteHeader()
ReadHeader()
The first four bytes of the deleted record is the record number to the next
deleted record in the chain
Append Record will pull next record from the chain and attempt to use that
field, otherwise it will append a new record
GetFirstRecord will skip over deleted records looking for the first record
which is not deleted
GetLastRecord will skip backwards to the next previous undeleted record
GetPrevRecord skips backwards to the the next previous undeleted record
DeleteRecord
-Deletes the memo data
- Adds the record to the front of the free chain
UndeleteRecord
- Always returns XB_INVALID_RECORD
PackDatafiles
- Deleted Records are skipped
NoOfRecords
- Returns no of records not deleted
PhysicalNoOfRecords()
- Return NoOfRecs - actual number of records in the file
Conclusions:
From a campatibility standpoint:
This setup will only work on the earlier version of the Xbase file format as this would
be library specific code.
Also, once past Dbase V3, the bytes used in the header file are used by Dbase 4,5,7
Decision:
In an effort to make the library as portable as possible moving forward, a decision was made to
leave this code out of the basic library. To add this code in the future, a new class can be created
using the xbDbf class as a base class, and override the methods mentioned above.
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