[Boost-bugs] [Boost C++ Libraries] #7971: [C++11] Boost::Format doesn't like to be fed nullptr/std::nullptr_t

Subject: [Boost-bugs] [Boost C++ Libraries] #7971: [C++11] Boost::Format doesn't like to be fed nullptr/std::nullptr_t
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2013-02-03 22:20:14

#7971: [C++11] Boost::Format doesn't like to be fed nullptr/std::nullptr_t
---------------------------------------------+------------------------------
 Reporter:  Roger Leigh <rleigh@…>           |       Owner:  samuel_krempp
     Type:  Bugs                             |      Status:  new          
Milestone:  To Be Determined                 |   Component:  format       
  Version:  Boost 1.50.0                     |    Severity:  Problem      
 Keywords:                                   |  
---------------------------------------------+------------------------------
 As the following code example shows, boost::format is not happy being fed
 a C++11 nullptr.  It would be nice if it could cope with this as a valid,
 but null, argument, e.g. equivalent to "", i.e. no output but a valid
 argument.  I've done this in my own code as a workaround for now by
 specialising for std::nullptr_t and then feeding it "" instead.  This
 might not be an issue with boost::format itself if this should be done
 elsewhere e.g. lexical_cast.

 Regards,
 Roger

 {{{
 #include <boost/format.hpp>
 #include <string>

 int main()
 {
   boost::format fmt("%1% %2% %3%\n");

   fmt % std::string("String") % 543 % nullptr;
 }
 }}}

 ==>

 {{{
 % g++ -std=c++11 -o test test.cc
 In file included from /usr/include/boost/format.hpp:49:0,
                  from test.cc:1:
 /usr/include/boost/format/feed_args.hpp: In instantiation of ‘void
 boost::io::detail::put_last(std::basic_ostream<_CharT, _Traits>&, const
 T&) [with Ch = char; Tr = std::char_traits<char>; T = std::nullptr_t]’:
 /usr/include/boost/format/feed_args.hpp:159:13:   required from ‘void
 boost::io::detail::put(T, const boost::io::detail::format_item<Ch, Tr,
 Alloc>&, typename boost::basic_format<Ch, Tr, Alloc>::string_type&,
 typename boost::basic_format<Ch, Tr, Alloc>::internal_streambuf_t&,
 boost::io::detail::locale_t*) [with Ch = char; Tr =
 std::char_traits<char>; Alloc = std::allocator<char>; T = std::nullptr_t&;
 typename boost::basic_format<Ch, Tr, Alloc>::string_type =
 std::basic_string<char>; typename boost::basic_format<Ch, Tr,
 Alloc>::internal_streambuf_t = boost::io::basic_altstringbuf<char,
 std::char_traits<char>, std::allocator<char> >;
 boost::io::detail::locale_t = std::locale]’
 /usr/include/boost/format/feed_args.hpp:253:17:   required from ‘void
 boost::io::detail::distribute(boost::basic_format<Ch, Tr, Alloc>&, T)
 [with Ch = char; Tr = std::char_traits<char>; Alloc =
 std::allocator<char>; T = std::nullptr_t&]’
 /usr/include/boost/format/feed_args.hpp:263:9:   required from
 ‘boost::basic_format<Ch, Tr, Alloc>&
 boost::io::detail::feed(boost::basic_format<Ch, Tr, Alloc>&, T) [with Ch =
 char; Tr = std::char_traits<char>; Alloc = std::allocator<char>; T =
 std::nullptr_t&]’
 /usr/include/boost/format/format_class.hpp:64:74:   required from
 ‘boost::basic_format<Ch, Tr, Alloc>& boost::basic_format<Ch, Tr,
 Alloc>::operator%(const T&) [with T = std::nullptr_t; Ch = char; Tr =
 std::char_traits<char>; Alloc = std::allocator<char>;
 boost::basic_format<Ch, Tr, Alloc> = boost::basic_format<char>]’
 test.cc:9:39:   required from here
 /usr/include/boost/format/feed_args.hpp:100:9: error: ambiguous overload
 for ‘operator<<’ in ‘os << x’
 /usr/include/boost/format/feed_args.hpp:100:9: note: candidates are:
 In file included from
 /usr/include/boost/format/detail/compat_workarounds.hpp:60:0,
                  from /usr/include/boost/format.hpp:27,
                  from test.cc:1:
 /usr/include/c++/4.7/ostream:106:7: note: std::basic_ostream<_CharT,
 _Traits>::__ostream_type& std::basic_ostream<_CharT,
 _Traits>::operator<<(std::basic_ostream<_CharT, _Traits>::__ostream_type&
 (*)(std::basic_ostream<_CharT, _Traits>::__ostream_type&)) [with _CharT =
 char; _Traits = std::char_traits<char>; std::basic_ostream<_CharT,
 _Traits>::__ostream_type = std::basic_ostream<char>]
 /usr/include/c++/4.7/ostream:115:7: note: std::basic_ostream<_CharT,
 _Traits>::__ostream_type& std::basic_ostream<_CharT,
 _Traits>::operator<<(std::basic_ostream<_CharT, _Traits>::__ios_type&
 (*)(std::basic_ostream<_CharT, _Traits>::__ios_type&)) [with _CharT =
 char; _Traits = std::char_traits<char>; std::basic_ostream<_CharT,
 _Traits>::__ostream_type = std::basic_ostream<char>;
 std::basic_ostream<_CharT, _Traits>::__ios_type = std::basic_ios<char>]
 /usr/include/c++/4.7/ostream:125:7: note: std::basic_ostream<_CharT,
 _Traits>::__ostream_type& std::basic_ostream<_CharT,
 _Traits>::operator<<(std::ios_base& (*)(std::ios_base&)) [with _CharT =
 char; _Traits = std::char_traits<char>; std::basic_ostream<_CharT,
 _Traits>::__ostream_type = std::basic_ostream<char>]
 /usr/include/c++/4.7/ostream:172:7: note: std::basic_ostream<_CharT,
 _Traits>::__ostream_type& std::basic_ostream<_CharT,
 _Traits>::operator<<(bool) [with _CharT = char; _Traits =
 std::char_traits<char>; std::basic_ostream<_CharT,
 _Traits>::__ostream_type = std::basic_ostream<char>]
 /usr/include/c++/4.7/ostream:243:7: note: std::basic_ostream<_CharT,
 _Traits>::__ostream_type& std::basic_ostream<_CharT,
 _Traits>::operator<<(const void*) [with _CharT = char; _Traits =
 std::char_traits<char>; std::basic_ostream<_CharT,
 _Traits>::__ostream_type = std::basic_ostream<char>]
 In file included from /usr/include/c++/4.7/ostream:607:0,
                  from
 /usr/include/boost/format/detail/compat_workarounds.hpp:60,
                  from /usr/include/boost/format.hpp:27,
                  from test.cc:1:
 /usr/include/c++/4.7/bits/ostream.tcc:121:5: note:
 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT,
 _Traits>::operator<<(std::basic_ostream<_CharT,
 _Traits>::__streambuf_type*) [with _CharT = char; _Traits =
 std::char_traits<char>; std::basic_ostream<_CharT,
 _Traits>::__streambuf_type = std::basic_streambuf<char>]
 In file included from
 /usr/include/boost/format/detail/compat_workarounds.hpp:60:0,
                  from /usr/include/boost/format.hpp:27,
                  from test.cc:1:
 /usr/include/c++/4.7/ostream:600:5: note: std::basic_ostream<_CharT,
 _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&&, const
 _Tp&) [with _CharT = char; _Traits = std::char_traits<char>; _Tp =
 std::nullptr_t] <near match>
 /usr/include/c++/4.7/ostream:600:5: note:   no known conversion for
 argument 1 from ‘std::basic_ostream<char>’ to ‘std::basic_ostream<char>&&’
 /usr/include/c++/4.7/ostream:546:5: note: std::basic_ostream<char,
 _Traits>& std::operator<<(std::basic_ostream<char, _Traits>&, const
 unsigned char*) [with _Traits = std::char_traits<char>]
 /usr/include/c++/4.7/ostream:541:5: note: std::basic_ostream<char,
 _Traits>& std::operator<<(std::basic_ostream<char, _Traits>&, const signed
 char*) [with _Traits = std::char_traits<char>]
 /usr/include/c++/4.7/ostream:528:5: note: std::basic_ostream<char,
 _Traits>& std::operator<<(std::basic_ostream<char, _Traits>&, const char*)
 [with _Traits = std::char_traits<char>]
 In file included from /usr/include/c++/4.7/ostream:607:0,
                  from
 /usr/include/boost/format/detail/compat_workarounds.hpp:60,
                  from /usr/include/boost/format.hpp:27,
                  from test.cc:1:
 /usr/include/c++/4.7/bits/ostream.tcc:323:5: note:
 std::basic_ostream<_CharT, _Traits>&
 std::operator<<(std::basic_ostream<_CharT, _Traits>&, const char*) [with
 _CharT = char; _Traits = std::char_traits<char>]
 }}}

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/7971>
Boost C++ Libraries <http://www.boost.org/>
Boost provides free peer-reviewed portable C++ source libraries.