Extracting data from file?

Hi, i'm reading a game format, it consists of two files one stores the file names, sizes and offsets of there location in the other file, the other holds the data. My problem is that i'm set at the offset where the data is but i dont know how to get it out into a seperate file. i think i need to use the file size in this but now sure. anyone got any ideas?

dest = WriteFile(chunk_name)
For i = 1 To chunk_size
	WriteByte(dest, ReadByte(src))
Next

Ok i'll try that, thanks.

Ok tryed it but it failed, not because of the code, it's because i've missed something along the line. I have an email with basic info that helped me, and also got some vb code of exporting the file but i dont understand it. would it be alright to post the code to see if anyone can understand it?
Thanks

[codebox][/codebox]

I've got some c++ code here that is meant to read and write the data by i dont understand it as i dont program in c++. Can anyone understand this:

// Open Raw File 
FILE* pFile = fopen("Oni.raw", "rb"); 
if(pFile == NULL) 
  return; 

// Seek to TXMP Data offset 
fseek(pFile, TxmpOffset, SEEK_SET); 

// Allocate buffer 
char* pBuffer = (char*)malloc(TxmpSize); 
if(pBuffer == NULL) 
{ 
  fclose(pFile); 
  return; 
} 

// Read Data 
fread(pBuffer, TxmpSize, 1, pFile); 

// Close source file 
fclose(pFile); 

// Open output file 
pFile = fopen("outfile.txmp", "wb") 
if(pFile == NULL) 
{ 
  free(pBuffer); 
  return; 
} 

// Write data 
fwrite(pBuffer, TxmpSize, 1, pFile); 

// Close output file 
fclose(pFile); 

// Free buffer 
free(pBuffer);

Thanks

Update to post.

That code snippet seems to simply open a file, seek to a specific position, read a specific number of bytes from that position into a buffer(bank), and finally write the buffer contents out to a second file.

The file position to read from and the number of bytes to be read are specified via TxmpOffset and TxmpSize, respectively. As these variables aren't defined in the code, I can't tell you what they are. :)

Ok, well i have the offset and the size of the txmp file already from some of my earlier coding for reading the dat file, Ok you said that it is store into a bank, does that mean that i have to do the same to get the correct data i want from the file i am reading?
Thanks

If you want to do the same as the above code (i.e. read data in from one file and write it out to another) then it'd be best to use a bank. Luckily, blitz makes it easy to read/write data between files and banks: take a look at the ReadBytes and WriteBytes commands (note the plural of 'Bytes' - these commands are different from the Read/WriteByte commands).

Ok well i've done what i think is right but i'm still not getting equaly compared data between the two files, it just looks completely different from the actual file that it is meant to be (When opened in a text editor) Don't know if anyone can follow my coding but i put it below for you to see, it now uses banks and the read and writebytes commands:

onifile=OpenFile("level0_Final.dat")
SeekFile(onifile,20)

;Read in the header
LibRecs = ReadInt(onifile)
Block1Recs = ReadInt(onifile)
Block2Recs = ReadInt(onifile)
DataStart = ReadInt(onifile)
DataSize = ReadInt(onifile)
NamesOffset = ReadInt(onifile)
NamesSize = ReadInt(onifile)
Unknown = ReadInt(onifile)*ReadInt(onifile)*ReadInt(onifile)*ReadInt(onifile)

Dim librecsdata$(librecs,8)

;read librecs
For Datasearch = 1 To Librecs
	librecsdata(datasearch,1) = Chr$(ReadByte(onifile)) + Chr$(ReadByte(onifile)) + Chr$(ReadByte(onifile)) + Chr$(ReadByte(onifile)) ;Lib type
	librecsdata(datasearch,2) = ReadInt(onifile) ;lib offset
	librecsdata(datasearch,3) = ReadInt(onifile) ;lib name offset
	librecsdata(datasearch,4) = ReadInt(onifile) ;lib size
	librecsdata(datasearch,5) = ReadShort(onifile) ;lib unknown1
	librecsdata(datasearch,6) = ReadShort(onifile) ;lib unknown2
Next

;Block Recs

SeekFile(onifile,NamesOffset)
For Dat = 1 To LibRecs

	librecsdata(dat,7) = "" ;dat type
	librecsdata(dat,8) = "" ;dat name

	librecsdata(dat,7) = Chr$(ReadByte(onifile)) + Chr$(ReadByte(onifile)) + Chr$(ReadByte(onifile)) + Chr$(ReadByte(onifile)) ;dat type data

	Repeat
		NameByte = ReadByte(onifile)
		If (NameByte <> 0)
			librecsdata(dat,8) = librecsdata(dat,8) + Chr$(Namebyte)
		EndIf
	Until NameByte = 0
	
	If (Eof(onifile))
		Exit
	EndIf


Next


For t= 1 To librecs
	If librecsdata(t,7) = "TXMP" And librecsdata(t,1) = "PMXT" Then
		Print ""
		Print "type: " + librecsdata(t,1)
		Print "offset: " + librecsdata(t,2)
		Print "Name Offset: " + librecsdata(t,3)
		Print "Size: " + librecsdata(t,4)
		Print "Unknown 1: " + librecsdata(t,5)
		Print "Unknown 2: " + librecsdata(t,6)
		Print "Extension: ." + librecsdata(t,7)
		Print "File name: " + librecsdata(t,8)
		Print "librec: " + t
	EndIf
Next

;get data from the raw file with reference from dat file
onirawfile=OpenFile("level0_Final.raw")
SeekFile(onirawfile, librecsdata(437,2));657672)

databuffer = CreateBank(librecsdata(437,4))
ReadBytes databuffer,onirawfile,0,librecsdata(437,4)

des = WriteFile(librecsdata(dat,8)+"."+librecsdata(dat,7))
WriteBytes databuffer,des,0,librecsdata(437,4)

I would have included in two files my exported file and the correctly exported file but thay are to big to even fit in a code box.
Thanks

Kain, I'll take a look at this tomorrow, when I get time. It's Friday night and I'm not 'in the right frame of mind'? ;)

Hmm, well, because I'm not familiar with the file formats you're working with, I'm not in a position help much. Sorry.

	librecsdata(datasearch,1) = Chr$(ReadByte(onifile)) + Chr$(ReadByte(onifile)) + Chr$(ReadByte(onifile)) + Chr$(ReadByte(onifile)) ;Lib type

You can't be sure that each of these bytes will be read from the file in that order. If you do something like ..

a$ = chr$( readbyte (onfile))
b$ = chr$( readbyte( onfile ) )
etc ....
liberectdata( datasearch, 1 ) = a$+b$

It may work.

Stevie

big10p, would it help if i sent you the dat file as that is only about 2Mb, The file i am working with the from the game oni which it would probably be quite easy to get hold of a demo of it. The site that i got the specs of the dat file was http://mirex.mypage.sk in documents and Unmass archives descriptions. If you can help any further with this information it would be most appreciated.
Thanks

Did you try implementing the changes Stevie G suggested?

Stevie G i applied your changes and still get the same result but from doing so and trying some things out i noticed that some of the data i have read in not correct to a program that can export these files, and it is to do with the typesfor example the sound files in the game should have the type DDNS but have some other one instead, i chaged some of the other code aswell to make it better but still not found out what causes the incorrect data.