[Boost-users] Variant stream output of ICU UnicodeString

9 Oct 2011

      Hi,
I'm trying to stream a Boost::Variant with << to std::cout but when I 
include an UnicodeString member from the ICU Unicode library the 
compiler doesn't recognices my overloaded operator<< for the UnicodeString.

Here is a test program:

#include <iostream>
#include <unicode/unistr.h>
#include <boost/variant.hpp>

class Foo {};

std::ostream& operator<<(std::ostream& stream, Foo const &b) {
return stream << "Foo";
}

std::ostream& operator<<(std::ostream& stream, UnicodeString const & 
unicode) {
return stream << "Unicode";
}

int main() {
boost::variant<Foo, UnicodeString, int, double> test;

test = Foo();
std::cout << test << std::endl;

test = "Hello World";
std::cout << test << std::endl;
return 0;
}

Without the UnicodeString code everything works find but with it I get 
the following errors:

g++ -O0 -g3 -Wall -c -fmessage-length=0 -MMD -MP -MF"src/TestUnicode.d" 
-MT"src/TestUnicode.d" -o "src/TestUnicode.o" "../src/TestUnicode.cpp"
In file included from /usr/include/boost/variant/variant.hpp:1859,
from /usr/include/boost/variant.hpp:17,
from ../src/TestUnicode.cpp:11:
/usr/include/boost/variant/detail/variant_io.hpp: In member function 
‘void boost::detail::variant::printer<OStream>::operator()(const T&) 
const [with T = icu_4_2::UnicodeString, OStream = 
std::basic_ostream<char, std::char_traits<char> >]’:
/usr/include/boost/variant/variant.hpp:825: instantiated from ‘typename 
Visitor::result_type 
boost::detail::variant::invoke_visitor<Visitor>::internal_visit(T&, int) 
[with T = const icu_4_2::UnicodeString, Visitor = 
boost::detail::variant::printer<std::basic_ostream<char, 
std::char_traits<char> > >]’
/usr/include/boost/variant/detail/visitation_impl.hpp:126: instantiated 
from ‘typename Visitor::result_type 
boost::detail::variant::visitation_impl_invoke_impl(int, Visitor&, 
VoidPtrCV, T*, mpl_::true_) [with Visitor = 
boost::detail::variant::invoke_visitor<boost::detail::variant::printer<std::basic_ostream<char, 
std::char_traits<char> > > >, VoidPtrCV = const void*, T = 
boost::detail::variant::visitation_impl(int, int, Visitor&, VoidPtrCV, 
mpl_::false_, NoBackupFlag, Which*, step0*) [with Which = 
boost::variant<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, 
T13, T14, T15, T16, T17, T18, T19>::internal_apply_visitor_impl(int, 
int, Visitor&, VoidPtrCV) [with Visitor = 
boost::detail::variant::invoke_visitor<boost::detail::variant::printer<std::basic_ostream<char, 
std::char_traits<char> > > >, VoidPtrCV = const void*, T0_ = Foo, T1 = 
icu_4_2::UnicodeString, T2 = int, T3 = double, T4 = 
boost::detail::variant::void_, T5 = boost::detail::variant::void_, T6 = 
boost::detail::variant::void_, T7 = boost::detail::variant::void_, T8 = 
boost::detail::variant::void_, T9 = boost::detail::variant::void_, T10 = 
boost::detail::variant::void_, T11 = boost::detail::variant::void_, T12 
= boost::detail::variant::void_, T13 = boost::detail::variant::void_, 
T14 = boost::detail::variant::void_, T15 = 
boost::detail::variant::void_, T16 = boost::detail::variant::void_, T17 
= boost::detail::variant::void_, T18 = boost::detail::variant::void_, 
T19 = boost::detail::variant::void_]::first_which, step0 = 
boost::variant<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, 
T13, T14, T15, T16, T17, T18, T19>::internal_apply_visitor_impl(int, 
int, Visitor&, VoidPtrCV) [with Visitor = 
boost::detail::variant::invoke_visitor<boost::detail::variant::printer<std::basic_ostream<char, 
std::char_traits<char> > > >, VoidPtrCV = const void*, T0_ = Foo, T1 = 
icu_4_2::UnicodeString, T2 = int, T3 = double, T4 = 
boost::detail::variant::void_, T5 = boost::detail::variant::void_, T6 = 
boost::detail::variant::void_, T7 = boost::detail::variant::void_, T8 = 
boost::detail::variant::void_, T9 = boost::detail::variant::void_, T10 = 
boost::detail::variant::void_, T11 = boost::detail::variant::void_, T12 
= boost::detail::variant::void_, T13 = boost::detail::variant::void_, 
T14 = boost::detail::variant::void_, T15 = 
boost::detail::variant::void_, T16 = boost::detail::variant::void_, T17 
= boost::detail::variant::void_, T18 = boost::detail::variant::void_, 
T19 = boost::detail::variant::void_]::first_step, Visitor = 
boost::detail::variant::invoke_visitor<boost::detail::variant::printer<std::basic_ostream<char, 
std::char_traits<char> > > >, VoidPtrCV = const void*, NoBackupFlag = 
boost::variant<Foo, icu_4_2::UnicodeString, int, double, 
boost::detail::variant::void_, boost::detail::variant::void_, 
boost::detail::variant::void_, boost::detail::variant::void_, 
boost::detail::variant::void_, boost::detail::variant::void_, 
boost::detail::variant::void_, boost::detail::variant::void_, 
boost::detail::variant::void_, boost::detail::variant::void_, 
boost::detail::variant::void_, boost::detail::variant::void_, 
boost::detail::variant::void_, boost::detail::variant::void_, 
boost::detail::variant::void_, 
boost::detail::variant::void_>::has_fallback_type_]::T1]’
/usr/include/boost/variant/detail/visitation_impl.hpp:169: instantiated 
from ‘typename Visitor::result_type 
boost::detail::variant::visitation_impl_invoke(int, Visitor&, VoidPtrCV, 
T*, NoBackupFlag, int) [with Visitor = 
boost::detail::variant::invoke_visitor<boost::detail::variant::printer<std::basic_ostream<char, 
std::char_traits<char> > > >, VoidPtrCV = const void*, T = 
boost::detail::variant::visitation_impl(int, int, Visitor&, VoidPtrCV, 
mpl_::false_, NoBackupFlag, Which*, step0*) [with Which = 
boost::variant<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, 
T13, T14, T15, T16, T17, T18, T19>::internal_apply_visitor_impl(int, 
int, Visitor&, VoidPtrCV) [with Visitor = 
boost::detail::variant::invoke_visitor<boost::detail::variant::printer<std::basic_ostream<char, 
std::char_traits<char> > > >, VoidPtrCV = const void*, T0_ = Foo, T1 = 
icu_4_2::UnicodeString, T2 = int, T3 = double, T4 = 
boost::detail::variant::void_, T5 = boost::detail::variant::void_, T6 = 
boost::detail::variant::void_, T7 = boost::detail::variant::void_, T8 = 
boost::detail::variant::void_, T9 = boost::detail::variant::void_, T10 = 
boost::detail::variant::void_, T11 = boost::detail::variant::void_, T12 
= boost::detail::variant::void_, T13 = boost::detail::variant::void_, 
T14 = boost::detail::variant::void_, T15 = 
boost::detail::variant::void_, T16 = boost::detail::variant::void_, T17 
= boost::detail::variant::void_, T18 = boost::detail::variant::void_, 
T19 = boost::detail::variant::void_]::first_which, step0 = 
boost::variant<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, 
T13, T14, T15, T16, T17, T18, T19>::internal_apply_visitor_impl(int, 
int, Visitor&, VoidPtrCV) [with Visitor = 
boost::detail::variant::invoke_visitor<boost::detail::variant::printer<std::basic_ostream<char, 
std::char_traits<char> > > >, VoidPtrCV = const void*, T0_ = Foo, T1 = 
icu_4_2::UnicodeString, T2 = int, T3 = double, T4 = 
boost::detail::variant::void_, T5 = boost::detail::variant::void_, T6 = 
boost::detail::variant::void_, T7 = boost::detail::variant::void_, T8 = 
boost::detail::variant::void_, T9 = boost::detail::variant::void_, T10 = 
boost::detail::variant::void_, T11 = boost::detail::variant::void_, T12 
= boost::detail::variant::void_, T13 = boost::detail::variant::void_, 
T14 = boost::detail::variant::void_, T15 = 
boost::detail::variant::void_, T16 = boost::detail::variant::void_, T17 
= boost::detail::variant::void_, T18 = boost::detail::variant::void_, 
T19 = boost::detail::variant::void_]::first_step, Visitor = 
boost::detail::variant::invoke_visitor<boost::detail::variant::printer<std::basic_ostream<char, 
std::char_traits<char> > > >, VoidPtrCV = const void*, NoBackupFlag = 
boost::variant<Foo, icu_4_2::UnicodeString, int, double, 
boost::detail::variant::void_, boost::detail::variant::void_, 
boost::detail::variant::void_, boost::detail::variant::void_, 
boost::detail::variant::void_, boost::detail::variant::void_, 
boost::detail::variant::void_, boost::detail::variant::void_, 
boost::detail::variant::void_, boost::detail::variant::void_, 
boost::detail::variant::void_, boost::detail::variant::void_, 
boost::detail::variant::void_, boost::detail::variant::void_, 
boost::detail::variant::void_, 
boost::detail::variant::void_>::has_fallback_type_]::T1, NoBackupFlag = 
boost::variant<Foo, icu_4_2::UnicodeString, int, double, 
boost::detail::variant::void_, boost::detail::variant::void_, 
boost::detail::variant::void_, boost::detail::variant::void_, 
boost::detail::variant::void_, boost::detail::variant::void_, 
boost::detail::variant::void_, boost::detail::variant::void_, 
boost::detail::variant::void_, boost::detail::variant::void_, 
boost::detail::variant::void_, boost::detail::variant::void_, 
boost::detail::variant::void_, boost::detail::variant::void_, 
boost::detail::variant::void_, 
boost::detail::variant::void_>::has_fallback_type_]’
/usr/include/boost/variant/detail/visitation_impl.hpp:256: instantiated 
from ‘typename Visitor::result_type 
boost::detail::variant::visitation_impl(int, int, Visitor&, VoidPtrCV, 
mpl_::false_, NoBackupFlag, Which*, step0*) [with Which = 
boost::variant<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, 
T13, T14, T15, T16, T17, T18, T19>::internal_apply_visitor_impl(int, 
int, Visitor&, VoidPtrCV) [with Visitor = 
boost::detail::variant::invoke_visitor<boost::detail::variant::printer<std::basic_ostream<char, 
std::char_traits<char> > > >, VoidPtrCV = const void*, T0_ = Foo, T1 = 
icu_4_2::UnicodeString, T2 = int, T3 = double, T4 = 
boost::detail::variant::void_, T5 = boost::detail::variant::void_, T6 = 
boost::detail::variant::void_, T7 = boost::detail::variant::void_, T8 = 
boost::detail::variant::void_, T9 = boost::detail::variant::void_, T10 = 
boost::detail::variant::void_, T11 = boost::detail::variant::void_, T12 
= boost::detail::variant::void_, T13 = boost::detail::variant::void_, 
T14 = boost::detail::variant::void_, T15 = 
boost::detail::variant::void_, T16 = boost::detail::variant::void_, T17 
= boost::detail::variant::void_, T18 = boost::detail::variant::void_, 
T19 = boost::detail::variant::void_]::first_which, step0 = 
boost::variant<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, 
T13, T14, T15, T16, T17, T18, T19>::internal_apply_visitor_impl(int, 
int, Visitor&, VoidPtrCV) [with Visitor = 
boost::detail::variant::invoke_visitor<boost::detail::variant::printer<std::basic_ostream<char, 
std::char_traits<char> > > >, VoidPtrCV = const void*, T0_ = Foo, T1 = 
icu_4_2::UnicodeString, T2 = int, T3 = double, T4 = 
boost::detail::variant::void_, T5 = boost::detail::variant::void_, T6 = 
boost::detail::variant::void_, T7 = boost::detail::variant::void_, T8 = 
boost::detail::variant::void_, T9 = boost::detail::variant::void_, T10 = 
boost::detail::variant::void_, T11 = boost::detail::variant::void_, T12 
= boost::detail::variant::void_, T13 = boost::detail::variant::void_, 
T14 = boost::detail::variant::void_, T15 = 
boost::detail::variant::void_, T16 = boost::detail::variant::void_, T17 
= boost::detail::variant::void_, T18 = boost::detail::variant::void_, 
T19 = boost::detail::variant::void_]::first_step, Visitor = 
boost::detail::variant::invoke_visitor<boost::detail::variant::printer<std::basic_ostream<char, 
std::char_traits<char> > > >, VoidPtrCV = const void*, NoBackupFlag = 
boost::variant<Foo, icu_4_2::UnicodeString, int, double, 
boost::detail::variant::void_, boost::detail::variant::void_, 
boost::detail::variant::void_, boost::detail::variant::void_, 
boost::detail::variant::void_, boost::detail::variant::void_, 
boost::detail::variant::void_, boost::detail::variant::void_, 
boost::detail::variant::void_, boost::detail::variant::void_, 
boost::detail::variant::void_, boost::detail::variant::void_, 
boost::detail::variant::void_, boost::detail::variant::void_, 
boost::detail::variant::void_, 
boost::detail::variant::void_>::has_fallback_type_]’
/usr/include/boost/variant/variant.hpp:1769: instantiated from ‘static 
typename Visitor::result_type boost::variant<T0, T1, T2, T3, T4, T5, T6, 
T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, T17, T18, 
T19>::internal_apply_visitor_impl(int, int, Visitor&, VoidPtrCV) [with 
Visitor = 
boost::detail::variant::invoke_visitor<boost::detail::variant::printer<std::basic_ostream<char, 
std::char_traits<char> > > >, VoidPtrCV = const void*, T0_ = Foo, T1 = 
icu_4_2::UnicodeString, T2 = int, T3 = double, T4 = 
boost::detail::variant::void_, T5 = boost::detail::variant::void_, T6 = 
boost::detail::variant::void_, T7 = boost::detail::variant::void_, T8 = 
boost::detail::variant::void_, T9 = boost::detail::variant::void_, T10 = 
boost::detail::variant::void_, T11 = boost::detail::variant::void_, T12 
= boost::detail::variant::void_, T13 = boost::detail::variant::void_, 
T14 = boost::detail::variant::void_, T15 = 
boost::detail::variant::void_, T16 = boost::detail::variant::void_, T17 
= boost::detail::variant::void_, T18 = boost::detail::variant::void_, 
T19 = boost::detail::variant::void_]’
/usr/include/boost/variant/variant.hpp:1791: instantiated from ‘typename 
Visitor::result_type boost::variant<T0, T1, T2, T3, T4, T5, T6, T7, T8, 
T9, T10, T11, T12, T13, T14, T15, T16, T17, T18, 
T19>::internal_apply_visitor(Visitor&) const [with Visitor = 
boost::detail::variant::invoke_visitor<boost::detail::variant::printer<std::basic_ostream<char, 
std::char_traits<char> > > >, T0_ = Foo, T1 = icu_4_2::UnicodeString, T2 
= int, T3 = double, T4 = boost::detail::variant::void_, T5 = 
boost::detail::variant::void_, T6 = boost::detail::variant::void_, T7 = 
boost::detail::variant::void_, T8 = boost::detail::variant::void_, T9 = 
boost::detail::variant::void_, T10 = boost::detail::variant::void_, T11 
= boost::detail::variant::void_, T12 = boost::detail::variant::void_, 
T13 = boost::detail::variant::void_, T14 = 
boost::detail::variant::void_, T15 = boost::detail::variant::void_, T16 
= boost::detail::variant::void_, T17 = boost::detail::variant::void_, 
T18 = boost::detail::variant::void_, T19 = boost::detail::variant::void_]’
/usr/include/boost/variant/variant.hpp:1813: instantiated from ‘typename 
Visitor::result_type boost::variant<T0, T1, T2, T3, T4, T5, T6, T7, T8, 
T9, T10, T11, T12, T13, T14, T15, T16, T17, T18, 
T19>::apply_visitor(Visitor&) const [with Visitor = 
boost::detail::variant::printer<std::basic_ostream<char, 
std::char_traits<char> > >, T0_ = Foo, T1 = icu_4_2::UnicodeString, T2 = 
int, T3 = double, T4 = boost::detail::variant::void_, T5 = 
boost::detail::variant::void_, T6 = boost::detail::variant::void_, T7 = 
boost::detail::variant::void_, T8 = boost::detail::variant::void_, T9 = 
boost::detail::variant::void_, T10 = boost::detail::variant::void_, T11 
= boost::detail::variant::void_, T12 = boost::detail::variant::void_, 
T13 = boost::detail::variant::void_, T14 = 
boost::detail::variant::void_, T15 = boost::detail::variant::void_, T16 
= boost::detail::variant::void_, T17 = boost::detail::variant::void_, 
T18 = boost::detail::variant::void_, T19 = boost::detail::variant::void_]’
/usr/include/boost/variant/detail/variant_io.hpp:85: instantiated from 
‘std::basic_ostream<_CharT, _Traits>& 
boost::operator<<(std::basic_ostream<_CharT, _Traits>&, const 
boost::variant<U0, U1, U2, U3, U4, U5, U6, U7, U8, U9, U10, U11, U12, 
U13, U14, U15, U16, U17, U18, U19>&) [with E = char, T = 
std::char_traits<char>, U0 = Foo, U1 = icu_4_2::UnicodeString, U2 = int, 
U3 = double, U4 = boost::detail::variant::void_, U5 = 
boost::detail::variant::void_, U6 = boost::detail::variant::void_, U7 = 
boost::detail::variant::void_, U8 = boost::detail::variant::void_, U9 = 
boost::detail::variant::void_, U10 = boost::detail::variant::void_, U11 
= boost::detail::variant::void_, U12 = boost::detail::variant::void_, 
U13 = boost::detail::variant::void_, U14 = 
boost::detail::variant::void_, U15 = boost::detail::variant::void_, U16 
= boost::detail::variant::void_, U17 = boost::detail::variant::void_, 
U18 = boost::detail::variant::void_, U19 = boost::detail::variant::void_]’
../src/TestUnicode.cpp:27: instantiated from here
/usr/include/boost/variant/detail/variant_io.hpp:64: error: no match for 
‘operator<<’ in ‘((const 
boost::detail::variant::printer<std::basic_ostream<char, 
std::char_traits<char> >
...
*)this)->boost::detail::variant::printer<std::basic_ostream<char, 
std::char_traits<char> > >::out_ << operand’
/usr/include/c++/4.4/ostream:108: note: candidates are: 
std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, 
_Traits>::operator<<(std::basic_ostream<_CharT, _Traits>& 
(*)(std::basic_ostream<_CharT, _Traits>&)) [with _CharT = char, _Traits 
= std::char_traits<char>]
/usr/include/c++/4.4/ostream:117: note: std::basic_ostream<_CharT, 
_Traits>& std::basic_ostream<_CharT, 
_Traits>::operator<<(std::basic_ios<_CharT, _Traits>& 
(*)(std::basic_ios<_CharT, _Traits>&)) [with _CharT = char, _Traits = 
std::char_traits<char>]
/usr/include/c++/4.4/ostream:127: note: std::basic_ostream<_CharT, 
_Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(std::ios_base& 
(*)(std::ios_base&)) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/include/c++/4.4/ostream:165: note: std::basic_ostream<_CharT, 
_Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(long int) 
[with _CharT = char, _Traits = std::char_traits<char>]
/usr/include/c++/4.4/ostream:169: note: std::basic_ostream<_CharT, 
_Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(long unsigned 
int) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/include/c++/4.4/ostream:173: note: std::basic_ostream<_CharT, 
_Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(bool) [with 
_CharT = char, _Traits = std::char_traits<char>]
/usr/include/c++/4.4/bits/ostream.tcc:91: note: 
std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, 
_Traits>::operator<<(short int) [with _CharT = char, _Traits = 
std::char_traits<char>]
/usr/include/c++/4.4/ostream:180: note: std::basic_ostream<_CharT, 
_Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(short unsigned 
int) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/include/c++/4.4/bits/ostream.tcc:105: note: 
std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, 
_Traits>::operator<<(int) [with _CharT = char, _Traits = 
std::char_traits<char>]
/usr/include/c++/4.4/ostream:191: note: std::basic_ostream<_CharT, 
_Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(unsigned int) 
[with _CharT = char, _Traits = std::char_traits<char>]
/usr/include/c++/4.4/ostream:200: note: std::basic_ostream<_CharT, 
_Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(long long int) 
[with _CharT = char, _Traits = std::char_traits<char>]
/usr/include/c++/4.4/ostream:204: note: std::basic_ostream<_CharT, 
_Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(long long 
unsigned int) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/include/c++/4.4/ostream:209: note: std::basic_ostream<_CharT, 
_Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(double) [with 
_CharT = char, _Traits = std::char_traits<char>]
/usr/include/c++/4.4/ostream:213: note: std::basic_ostream<_CharT, 
_Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(float) [with 
_CharT = char, _Traits = std::char_traits<char>]
/usr/include/c++/4.4/ostream:221: note: std::basic_ostream<_CharT, 
_Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(long double) 
[with _CharT = char, _Traits = std::char_traits<char>]
/usr/include/c++/4.4/ostream:225: note: std::basic_ostream<_CharT, 
_Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(const void*) 
[with _CharT = char, _Traits = std::char_traits<char>]
/usr/include/c++/4.4/bits/ostream.tcc:119: note: 
std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, 
_Traits>::operator<<(std::basic_streambuf<_CharT, _Traits>*) [with 
_CharT = char, _Traits = std::char_traits<char>]
I'm using gcc 4.4.5 on Ubuntu 11.04 and boost 1.42.
Does someone know why the overloaded operator isn't used or how I can 
get the test program to work?

[Boost-users] Variant stream output of ICU UnicodeString

André