Re: [Boost-users] boost::filesystem problems

From: Victor A. Wagner Jr. (vawjr_at_[hidden])
Date: 2004-08-18 09:31:38

Adding exception safety in the "succeeds or has no effect" to copy_file 
certainly seem like reasonable suggestion.  It adds a small complication of 
creating a temporary file first, but I'd say it was generally worth 
it.  Note that _could_ change the behavior of some programs that are 
correctly functioning now in very limited "file space" and make them 
inoperative.

At Wednesday 2004-08-18 05:19, you wrote:
>On Tue, Aug 17, 2004 at 11:55:22PM -0700, Victor A. Wagner Jr. wrote:
> > At Tuesday 2004-08-17 17:16, you wrote:
> > >On Tue, Aug 17, 2004 at 02:40:14PM -0700, Delfin Rojas wrote:
> > >> Hi Carlo,
> > >>
> > >> I just wanted to point out native_file_string is part of
> > >> boost::filesystem::path and copy_file and rename_file (actually called
> > >> rename) are part of boost::filesystem (operations.hpp).
> > >
> > >I am aware of that.  The point is that I had a need to rewrite them.
> > >That seems to indicate that the boost implementation is flawed.
> >
> > perhaps you could enlighten us further?
> > "doesn't work" is a lousy bug report
> > "flawed" isn't a lot better.
>
>My problem is that Beman is not here.  It seems to make little
>sense to try to convince people when in the end nobody is going
>to make changes to boost when he is not here.
>
>But I can tell you what I improved of course.  Lets start with
>just one case.
>
>boost::filesystem::copy_file starts with truncating the target
>file - and when an error occurs, it throws - but STILL did truncate
>the target file (assuming it already existed) (the exception at
>the bottom of the function).
>
>This is not how I want exceptions to work; when an exception is
>thrown from a function then nothing must have been changed - as
>if the exception is thrown at the start of the function.
>
>My implementation of copy_file either succeeds completely or doesn't
>do anything: it is atomic.
>
>I need this for robustness.  I don't write applications that '"Oops"
>some error occured - sorry, your configuration file was erased - no
>there is no backup, I was trying to make one namely'.  I have a gard my
>reputation to write robust and bug free code ;).
>
>The other changes are mostly also related to the need for a better
>defined post-condition in case of errors.
>
>--
>Carlo Wood <carlo_at_[hidden]>
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Victor A. Wagner Jr.      http://rudbek.com
The five most dangerous words in the English language:
               "There oughta be a law"