[LC++]Copying files and deleting directories

[Krishna Monian]

What is a decent sized buffer? About 10K?

Regarding the mmap option, would you able to direct me
to a place that has a good tutorial on it, with some
sample code.

Thanks a lot
Krishna Monian

--- Paul Gearon <gearon at ieee.org> wrote:

> On 10/09/2004, at 7:33 AM, Krishna Monian wrote:
> 
> > Hi,
> > So what is the best way to implement my own
> version of
> > copy?
> >
> > Currently, I open the file, read a certain number
> of
> > bytes into a buffer and then write it into the
> file
> > until I am done. This is a very lame way I would
> say.
> 
> No, that's just fine.  Just make sure that the size
> of your buffer 
> isn't tiny, else you'll call read and write too
> often.  IIRC cp uses 
> this method for small files.  Whatever you do, don't
> use fread and 
> fwrite.
> 
> For larger files cp uses mmap.  To do this, you just
> map the source 
> file, then you create, expand, and map the
> destination file, and 
> finally you do a memcpy from one map to the other. 
> It's actually quite 
> easy to do.  This method has more overhead to set
> up, but skips a 
> memory copy of the data (which is why it's faster
> for large files).
> 
> > I might have several files to copy at a time
> (1000s).
> > From your discussion it seems that the system
> function
> > will be relatively slow for this purpose.
> 
> If you have lots of files, then set up time is
> important.  If the files 
> are small, then using read/write would probably
> offer the best option 
> here.
> 
> > Is there some better way to go about doing this?
> It
> > doesn't have to faster than cp. Anything faster
> than
> > my current method is acceptable.
> 
> Just use a read/write loop on a decent sized buffer.
>  If you discover 
> that it's too slow for what you need, then you can
> look at optimising 
> with mmap.  Don't fall into the pre-optimising trap!
> 
> Regards,
> Paul Gearon
> 
> Software Engineer
> Tucana Technologies
> http://www.tucanatech.com
> 
> Catapultam habeo. Nisi pecuniam omnem mihi dabis, ad
> caput tuum saxum
> immane mittam.
> (Translation from latin: "I have a catapult. Give me
> all the money,
> or I will fling an enormous rock at your head.")
> 
> 
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