Win a copy of The Little Book of Impediments (e-book only) this week in the Agile and Other Processes forum!
  • Post Reply
  • Bookmark Topic Watch Topic
  • New Topic

Last Record in Database File

 
Neo Say Bin
Greenhorn
Posts: 7
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Hi All,

I got the B&S assignment and I have a question regarding the database file.

My assignment states the following data file format:

Start of file
4 byte numeric, magic cookie value. Identifies this as a data file
2 byte numeric, number of fields in each record

Schema description section.
Repeated for each field in a record:
1 byte numeric, length in bytes of field name
n bytes (defined by previous entry), field name
1 byte numeric, field length in bytes
end of repeating block

Data section.
Repeat to end of file:
1 byte flag. 00 implies valid record, 0xFF implies deleted record
Record containing fields in order specified in schema section, no separators between fields, each field fixed length at maximum specified in schema information

End of file

All numeric values are stored in the header information use the formats of the DataInputStream and DataOutputStream classes. All text values, and all fields (which are text only), contain only 8 bit characters, null terminated if less than the maximum length for the field. The character encoding is 8 bit US ASCII.


When I execute the application, I deduce that:

My database length is size 6093, with header size 55.
Each data record is size 183.

For the last data record stored in the database file, the size is only 182. It seems there is a missing 1 byte flag for my last data record.

Is this normal? How should I handle this last data record that seems to have a missing 1 byte flag?

I'm asking this question as I have problems determining the offset for adding a new record.


Thank you for the help. Regards.
 
Anne Crace
Ranch Hand
Posts: 223
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Are you looking at it in a hex editor? It sounds like you are, if you have figured out the length of the DB and the records. My flag is at the beginning of the record, and it looks like yours is, too. I don't think it is the flag that is missing. Get a hex editor, if you aren't already using one. It will clear up a lot of questions.
 
Robert James Liguori
Author
Ranch Hand
Posts: 553
5
Java Netbeans IDE Oracle
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Cygnus is a good hex editor for Windows.

http://www.softcircuits.com/cygnus/
 
  • Post Reply
  • Bookmark Topic Watch Topic
  • New Topic