Pak Files?

[xGTx]

Well, i've been messing with file handling trying to learn it real well, and im curious... When I write a string to the filestream like:

Stream.Write('asd',66785);

What's all those random characters it writes to the file after 'asd' since the buffer is 3 chars long, not 66785.?

[Paulius]

Write writes the number of bytes you tell it to, if you're variable is only 3 bytes long and you attempt to write 66785 bytes then if not causing an access violation you'll also write 66782 bytes of whatever is in memory after your variable.

[xGTx]

Thanks.

Back onto my pak file question and from what alimonster wrote:

How do i find the location of my file headers? Since every file is suppose to be put in the top of the package file one after another and I add all the file information at the end like you said, how do i locate those at the end?

[cairnswm]

Out of interest have you thought of using a Zip file to store the information. The dzlib components have a method to read the zipped file directly into a stream thereby not leaving anything on the hard disk.

[Paulius]

Store you're file header count at the end of the file, then when reading seek to the end of the stream ?¢_" sizeof(integer) and read the header count, seek back NumberOfHeaders * sizeof(THeader) and there you are.

[xGTx]

Thanks Paulius.

Cairns, I have thought about it, but would just much rather learn this part my own.

[xGTx]

Ok i think i have most this technique down. But 1 question left.

When adding a file to a pack, I write the actual file data at the end of all the other file data, but above the headers. This position can be found by reading all the existing headers and just adding together the filesizes. After adding that data, you then add a header for that data at the very bottom of the file, leaving a few bytes to store how many headers there are at the very end of the file. Correct?

My question is, more of a clarification.... To write a file to a certian spot in a file, i simple to Stream.SeekTo(0, AllOfHeaderSizesAdded); then Stream.WriteBuffer(NewFileStream, Length(NewFileStream); ?

[Harry Hunt]

Almost correct, the Seek method takes two parameters, the first one is the Position in the stream (so AllOfHeaderSizesAdded) and the second parameter tells the method where to start counting. The second parameter can for example be soFromBeginning or soFromEnd so
Seek(23653, soFromBeginning) seeks to the 23653rd byte from the beginning of the file.

Also, your package files consist of three individual parts: the file data at the beginning, a list of all files and a footer which stores the file count.

When you want to append files to your package, you'll have to seek to the position right after the last file in the package and then write the new file there. You will then have to re-build the entire file index and the footer so it's a good idea to create a copy of the index list before appending a file.

Here's an image that should clarify the structure of a package file for you

[xGTx]

And how do i write a file in at an exact position? (Just so i dont mess this up)

[Harry Hunt]

[pascal]
var
PackageStream, FileStream: TFileStream;
BehindLastFile: Int64;
begin
{...}
FileStream.Create('C:\somefile.abc', fmOpenRead);
FileStream.Seek(0, soFromBeginning);
PackageStream.Seek(BehindLastFile, soFromBeginning);
PackageStream.CopyFrom(FileStream, FileStream.Size);
FileStream.Free;
ReBuildFileIndex;
ReBuildFooter;
end;
[/pascal]