Re: [boost] [filesystem] Possible problem in copy_file

From: Beman Dawes (bdawes_at_[hidden])
Date: 2006-02-07 18:12:42

G. Wade Johnson wrote:
> I was looking in the code for copy_file() and noticed what may be a bug. In
> the loop that handles partial writes, the code makes multiple attempts
> reducing the amount of data written each time. Unfortunately, the offset into
> the data is not changed as well. See below.
> 
>         sz_write = 0;
>         do
>         {
>           if ( (sz = ::write( outfile, buf.get(), sz_read - sz_write )) < 0 )
>           { 
>             sz_read = sz; // cause read loop termination
>             break;        //  and error to be thrown after closes
>           }
>           sz_write += sz;
>         } while ( sz_write < sz_read );
> 
> Unless I'm missing something, it looks like a partial write will result in the
> first part of the buffer being written multiple times. I checked the version
> in CVS and it appears to have the same code.
> 
> Am I missing something or is this incorrect?

A bug for sure. Nice catch. Fixed in CVS.

At least I hope it is fixed. I don't see an easy way to test it.

The code now reads:

           sz_write = 0;
           do
           {
             if ( (sz = ::write( outfile, buf.get()+sz_write,
               sz_read - sz_write )) < 0 )
             {
               sz_read = sz; // cause read loop termination
               break;        //  and error to be thrown after closes
             }
             sz_write += sz;
           } while ( sz_write < sz_read );

Thanks,

--Beman