Re: Do not take address of empty string front

[Jonathan Wakely <jwakely at redhat dot com>]

On 23/06/15 22:04 +0200, François Dumont wrote:
> On 22/06/2015 17:10, Jonathan Wakely wrote:
> > On 20/06/15 12:59 +0100, Jonathan Wakely wrote:
> > > On 20/06/15 12:03 +0200, François Dumont wrote:
> > > > Hi
> > > >
> > > >   2 experimental tests are failing in debug mode because
> > > > __do_str_codecvt is sometimes taking address of string front() and
> > > > back() even if empty. It wasn't use so not a big issue but it still
> > > > seems better to avoid. I propose to rather use string begin() to get
> > > > buffer address.
> > >
> > > But derefencing begin() is still undefined for an empty string.
> > > Shouldn't that fail for debug mode too? Why change one form of
> > > undefined behaviour that we diagnose to another form that we don't
> > > diagnose?
> > >
> > > It would be better if that function didn't do any work when the input
> > > range is empty:
> > >
> > > --- a/libstdc++-v3/include/bits/locale_conv.h
> > > +++ b/libstdc++-v3/include/bits/locale_conv.h
> > > @@ -58,6 +58,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> > >                    _OutStr& __outstr, const _Codecvt& __cvt, _State&
> > > __state,
> > >                    size_t& __count, _Fn __fn)
> > >    {
> > > +      if (__first == __last)
> > > +       {
> > > +         __outstr.clear();
> > > +         return true;
> > > +       }
> > > +
>
> Shouldn't it also set __count to 0 to make clear that nothing has been
> converted.

Yes, thanks. Fixed like so.

Tested powerpc64le-linux, in debug and normal modes, committed to trunk.


commit f02e0e6dfd0ffbef53252aa0b739a9b1ba7391ff
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Thu Jun 25 14:51:19 2015 +0100

    	* include/bits/locale_conv.h (__do_str_codecvt): Set __count.

diff --git a/libstdc++-v3/include/bits/locale_conv.h b/libstdc++-v3/include/bits/locale_conv.h
index fd99499..146f78b 100644
--- a/libstdc++-v3/include/bits/locale_conv.h
+++ b/libstdc++-v3/include/bits/locale_conv.h
@@ -61,6 +61,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       if (__first == __last)
 	{
 	  __outstr.clear();
+	  __count = 0;
 	  return true;
 	}