Re: How to split a compressed file programmatically?

On 29 oct, 15:15, Peter Duniho <NpOeStPe...@xxxxxxxxxxxxxxxx> wrote:
On 2007-10-29 07:45:46 -0700, Brian Roisentul
<brianroisen...@xxxxxxxxxxx> said:

BTW, this is my code, maybe i did something wrong:

The most serious issue I see is that you don't properly account for the
fractional remainder of the file when you calculate the number of
parts. Your division will return the number of full-size partitions of
the file, but in most cases you'll have some extra bytes at the end
that you're not saving.

You should keep track of how many bytes you've actually written, and
then after writing out the full-size partitions, write a final
partition that's whatever's less. Personally, I would forget about the
calculation altogether and just write a loop that keeps writing bytes
in chunks as large as you want or however many bytes you have
remaining, whichever is less, until you have no more bytes to write.
But how exactly you do this isn't so important as making sure you do it
right.

There are other things about the code that are less-than-perfect (a
couple of examples are mentioned after this paragraph), but as near as
I can tell, the above is the most serious problem. I didn't bother to
inspect the code that reconstructs the file, but assuming it was
written with similar care as the code that splits the file, it likely
has problems too.

I'm a bit bewildered at the "long.Parse(size_part.ToString())"
business. The "size_part" variable is already a long; what possible
value is there in converting that to a string and then back to a long?

You also have a strange calculation that screws up the "offset"
variable; it turns out not to matter because you don't really need the
variable at all. But it's still odd.

And why allocate a new buffer for each chunk you want to write, and why
does that buffer have to be the length of the original file, and given
that you're allocating a new buffer each time, why read the data
anywhere other than the beginning of the buffer?

For splitting the file, I would recommend code that looks more like this:

void splitFile(string path, string path_parts, int size_part)
{
using (FileStream fs = new FileStream(path, FileMode.Open))
{
int ipart = 0;
byte[] arrBytes = new byte[size_part];
int cbRead;

while ((cbRead = fs.Read(arrBytes, 0, size_part)) > 0)
{
string filename = Path.Combine(path_parts,
Path.GetFilenameWithoutExtension(path) + ipart.ToString() + this.ext);

using (FileStream fsOut = new FileStream(filename,
FileMode.Create))
{
fsOut.Write(arrBytes, 0, cbRead);
}

ipart++;
}
}
}

In other words, just read chunks of the original file until you can't
read any more, writing them out one by one, each to a new file.

Reading the parts and reconstructing the file should be similarly
simple. And remember, the more complicated you make the code, the
easier it is to create a bug in the code. The single most important
thing you can do to ensure your code is correct and free of bugs is to
make it as simple as you can.

Pete

It worked!

Thanks for taking your time and for your good explanation. I learn a
lot from these kind of things.

I'm only 20 and I don't have much time programming, so i'm working
every day on improving my level.

Thanks everyone for helping :)

.

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