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All numeric values are stored in the header information

paul seldon
Greenhorn

Joined: Oct 26, 2006
Posts: 13
"Header Information"
Is it from the start of the file to right before schema section,
right? When I print *.db file it comes out like below :
------------------------------------------------------------------------
< Instruction.html >
-> Start of file
4 byte numeric, magic cookie value. Identifies this as a data file
4 byte numeric, total overall length in bytes of each record
2 byte numeric, number of fields in each record

Schema description section.

------------------------------------------------------------------
< Result after reading dataInputStream>

Cookie value(4Byte) : 513
OveralLength(4Byte) : 183
NumberOfField(2Byte): 6

Each Record has :
name : 32
location : 64
specialties : 64
size : 6
rate : 8
owner : 8
Head Size : 70
----------------------------------------------------------------

70 means what? 70 byte for all header information?
How should I think of this?

Let me know. Thanks -
Benjamin Wang
Greenhorn

Joined: Sep 30, 2006
Posts: 5
yes

We have same magic cookie value and header length.
Keith Jones
Ranch Hand

Joined: Oct 30, 2006
Posts: 105
I wonder how you came to that cookie value. Mine is:

first byte: 0
second byte: 0
third byte: 2
forth byte: 3

I was also wondering if we have to check this value whenever reading the file. In other words do we have to say:

if (magicCookieValue equals "something") {
proceed
}
else {
error
}


SCJP 1.4
Mihai Radulescu
Ranch Hand

Joined: Sep 18, 2003
Posts: 918

Hi,

A small tip - uses a hex editor to peek in to the db file, you'll easily get your cookie.
The cookie purpose is to identify a valid database file, this because each database can have a different structure, by example in my scheme :

1 byte flag. 00 implies valid record, 0xFF implies deleted record


but I know other scheme with different values.

Regards M


SCJP, SCJD, SCWCD, OCPJBCD
Mark Smyth
Ranch Hand

Joined: Feb 04, 2004
Posts: 288
Originally posted by Keith Jones:
I wonder how you came to that cookie value. Mine is:

first byte: 0
second byte: 0
third byte: 2
forth byte: 3

I was also wondering if we have to check this value whenever reading the file. In other words do we have to say:

if (magicCookieValue equals "something") {
proceed
}
else {
error
}


You need to read the four bytes together as an integer value rather than as 4 consectutive bytes to get the magic cookie value. Use the readInt() method to do this.


SCJP<br />SCJD
 
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subject: All numeric values are stored in the header information