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Asked: 2026-06-12T15:11:22+00:00

I can’t compile the last line for the following code: typedef boost::variant<std::vector<int8_t>, std::vector<std::string>> Container;

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I can’t compile the last line for the following code: 

typedef boost::variant<std::vector<int8_t>, std::vector<std::string>> Container; 

std::vector<std::string> v1;
v1.push_back("sd");
Container c1;
c1 = v1;

std::vector<int8_t> v2;
v2.push_back(1);
v2.push_back(2);
Container c2;
c2 = v2;

EXPECT_EQ(c1,c2);

However, if I replace it with this line, it works:

EXPECT_EQ(c1==c2,true);

EXPECT_EQ is a function from Google Test.

What is the issue here?

The compiler error in VS2010 is as follows:

1>          c:\gtest-1.6.0\include\gtest\gtest-printers.h(338) : see reference to function template instantiation 'void testing_internal::DefaultPrintNonContainerTo<T>(const T &,std::ostream *)' being compiled
1>          with
1>          [
1>              T=Com::ObjRepWrap::Container
1>          ]
1>          c:\gtest-1.6.0\include\gtest\gtest-printers.h(376) : see reference to function template instantiation 'void testing::internal::DefaultPrintTo<T>(testing::internal::IsNotContainer,testing::internal::false_type,const T &,std::ostream *)' being compiled
1>          with
1>          [
1>              T=Com::ObjRepWrap::Container
1>          ]
1>          c:\gtest-1.6.0\include\gtest\gtest-printers.h(600) : see reference to function template instantiation 'void testing::internal::PrintTo<T>(const T &,std::ostream *)' being compiled
1>          with
1>          [
1>              T=Com::ObjRepWrap::Container
1>          ]
1>          c:\gtest-1.6.0\include\gtest\gtest-printers.h(591) : while compiling class template member function 'void testing::internal::UniversalPrinter<T>::Print(const T &,std::ostream *)'
1>          with
1>          [
1>              T=Com::ObjRepWrap::Container
1>          ]
1>          c:\gtest-1.6.0\include\gtest\gtest-printers.h(697) : see reference to class template instantiation 'testing::internal::UniversalPrinter<T>' being compiled
1>          with
1>          [
1>              T=Com::ObjRepWrap::Container
1>          ]
1>          c:\gtest-1.6.0\include\gtest\gtest-printers.h(678) : see reference to function template instantiation 'void testing::internal::UniversalPrint<T>(const T &,std::ostream *)' being compiled
1>          with
1>          [
1>              T=Com::ObjRepWrap::Container
1>          ]
1>          c:\gtest-1.6.0\include\gtest\gtest-printers.h(790) : see reference to function template instantiation 'void testing::internal::UniversalTersePrint<T>(const T &,std::ostream *)' being compiled
1>          with
1>          [
1>              T=Com::ObjRepWrap::Container
1>          ]
1>          c:\gtest-1.6.0\include\gtest\gtest.h(1301) : see reference to function template instantiation 'std::string testing::PrintToString<T1>(const T &)' being compiled
1>          with
1>          [
1>              T1=Com::ObjRepWrap::Container,
1>              T=Com::ObjRepWrap::Container
1>          ]
1>          c:\gtest-1.6.0\include\gtest\gtest.h(1326) : see reference to function template instantiation 'testing::internal::String testing::internal::FormatForComparisonFailureMessage<T1,T2>(const T1 &,const T2 &)' being compiled
1>          with
1>          [
1>              T1=Com::ObjRepWrap::Container,
1>              T2=Com::ObjRepWrap::Container
1>          ]
1>          c:\gtest-1.6.0\include\gtest\gtest.h(1353) : see reference to function template instantiation 'testing::AssertionResult testing::internal::CmpHelperEQ<T1,T2>(const char *,const char *,const T1 &,const T2 &)' being compiled
1>          with
1>          [
1>              T1=Com::ObjRepWrap::Container,
1>              T2=Com::ObjRepWrap::Container
1>          ]
1>          c:\visual studio 2010\projects\db\xxx\main.cpp(127) : see reference to function template instantiation 'testing::AssertionResult testing::internal::EqHelper<lhs_is_null_literal>::Compare<Com::ObjRepWrap::Container,Com::ObjRepWrap::Container>(const char *,const char *,const T1 &,const T2 &)' being compiled
1>          with
1>          [
1>              lhs_is_null_literal=false,
1>              T1=Com::ObjRepWrap::Container,
1>              T2=Com::ObjRepWrap::Container
1>          ]
1>c:\boost_1_49_0\boost\variant\detail\variant_io.hpp(64): error C2679: binary '<<' : no operator found which takes a right-hand operand of type 'const T1' (or there is no acceptable conversion)
1>          c:\program files\microsoft visual studio 10.0\vc\include\ostream(679): could be 'std::basic_ostream<_Elem,_Traits> &std::operator <<<char,std::char_traits<char>>(std::basic_ostream<_Elem,_Traits> &,const char *)' [found using argument-dependent lookup]
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]
1>          c:\program files\microsoft visual studio 10.0\vc\include\ostream(726): or       'std::basic_ostream<_Elem,_Traits> &std::operator <<<char,std::char_traits<char>>(std::basic_ostream<_Elem,_Traits> &,char)' [found using argument-dependent lookup]
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]
1>          c:\program files\microsoft visual studio 10.0\vc\include\ostream(764): or       'std::basic_ostream<_Elem,_Traits> &std::operator <<<std::char_traits<char>>(std::basic_ostream<_Elem,_Traits> &,const char *)' [found using argument-dependent lookup]
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]
1>          c:\program files\microsoft visual studio 10.0\vc\include\ostream(811): or       'std::basic_ostream<_Elem,_Traits> &std::operator <<<std::char_traits<char>>(std::basic_ostream<_Elem,_Traits> &,char)' [found using argument-dependent lookup]
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]
1>          c:\program files\microsoft visual studio 10.0\vc\include\ostream(937): or       'std::basic_ostream<_Elem,_Traits> &std::operator <<<std::char_traits<char>>(std::basic_ostream<_Elem,_Traits> &,const signed char *)' [found using argument-dependent lookup]
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]
1>          c:\program files\microsoft visual studio 10.0\vc\include\ostream(944): or       'std::basic_ostream<_Elem,_Traits> &std::operator <<<std::char_traits<char>>(std::basic_ostream<_Elem,_Traits> &,signed char)' [found using argument-dependent lookup]
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]
1>          c:\program files\microsoft visual studio 10.0\vc\include\ostream(951): or       'std::basic_ostream<_Elem,_Traits> &std::operator <<<std::char_traits<char>>(std::basic_ostream<_Elem,_Traits> &,const unsigned char *)' [found using argument-dependent lookup]
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]
1>          c:\program files\microsoft visual studio 10.0\vc\include\ostream(958): or       'std::basic_ostream<_Elem,_Traits> &std::operator <<<std::char_traits<char>>(std::basic_ostream<_Elem,_Traits> &,unsigned char)' [found using argument-dependent lookup]
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]
1>          c:\program files\microsoft visual studio 10.0\vc\include\ostream(968): or       'std::basic_ostream<_Elem,_Traits> &std::operator <<<char,std::char_traits<char>,T>(std::basic_ostream<_Elem,_Traits> &&,_Ty)' [found using argument-dependent lookup]
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>,
1>              T=T1,
1>              _Ty=T1
1>          ]
1>          c:\program files\microsoft visual studio 10.0\vc\include\ostream(1085): or       'std::basic_ostream<_Elem,_Traits> &std::operator <<<char,std::char_traits<char>>(std::basic_ostream<_Elem,_Traits> &,const std::error_code &)' [found using argument-dependent lookup]
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]
1>          c:\boost_1_49_0\boost\blank.hpp(93): or       'std::basic_ostream<_Elem,_Traits> &boost::operator <<<char,std::char_traits<char>>(std::basic_ostream<_Elem,_Traits> &,const boost::blank &)'
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]
1>          c:\program files\microsoft visual studio 10.0\vc\include\ostream(186): or       'std::basic_ostream<_Elem,_Traits> &std::basic_ostream<_Elem,_Traits>::operator <<(std::basic_ostream<_Elem,_Traits> &(__cdecl *)(std::basic_ostream<_Elem,_Traits> &))'
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]
1>          c:\program files\microsoft visual studio 10.0\vc\include\ostream(192): or       'std::basic_ostream<_Elem,_Traits> &std::basic_ostream<_Elem,_Traits>::operator <<(std::basic_ios<_Elem,_Traits> &(__cdecl *)(std::basic_ios<_Elem,_Traits> &))'
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]
1>          c:\program files\microsoft visual studio 10.0\vc\include\ostream(199): or       'std::basic_ostream<_Elem,_Traits> &std::basic_ostream<_Elem,_Traits>::operator <<(std::ios_base &(__cdecl *)(std::ios_base &))'
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]
1>          c:\program files\microsoft visual studio 10.0\vc\include\ostream(206): or       'std::basic_ostream<_Elem,_Traits> &std::basic_ostream<_Elem,_Traits>::operator <<(std::_Bool)'
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]
1>          c:\program files\microsoft visual studio 10.0\vc\include\ostream(226): or       'std::basic_ostream<_Elem,_Traits> &std::basic_ostream<_Elem,_Traits>::operator <<(short)'
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]
1>          c:\program files\microsoft visual studio 10.0\vc\include\ostream(260): or       'std::basic_ostream<_Elem,_Traits> &std::basic_ostream<_Elem,_Traits>::operator <<(unsigned short)'
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]
1>          c:\program files\microsoft visual studio 10.0\vc\include\ostream(280): or       'std::basic_ostream<_Elem,_Traits> &std::basic_ostream<_Elem,_Traits>::operator <<(int)'
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]
1>          c:\program files\microsoft visual studio 10.0\vc\include\ostream(305): or       'std::basic_ostream<_Elem,_Traits> &std::basic_ostream<_Elem,_Traits>::operator <<(unsigned int)'
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]
1>          c:\program files\microsoft visual studio 10.0\vc\include\ostream(325): or       'std::basic_ostream<_Elem,_Traits> &std::basic_ostream<_Elem,_Traits>::operator <<(long)'
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]
1>          c:\program files\microsoft visual studio 10.0\vc\include\ostream(345): or       'std::basic_ostream<_Elem,_Traits> &std::basic_ostream<_Elem,_Traits>::operator <<(unsigned long)'
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]
1>          c:\program files\microsoft visual studio 10.0\vc\include\ostream(366): or       'std::basic_ostream<_Elem,_Traits> &std::basic_ostream<_Elem,_Traits>::operator <<(__int64)'
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]
1>          c:\program files\microsoft visual studio 10.0\vc\include\ostream(386): or       'std::basic_ostream<_Elem,_Traits> &std::basic_ostream<_Elem,_Traits>::operator <<(unsigned __int64)'
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]
1>          c:\program files\microsoft visual studio 10.0\vc\include\ostream(407): or       'std::basic_ostream<_Elem,_Traits> &std::basic_ostream<_Elem,_Traits>::operator <<(float)'
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]
1>          c:\program files\microsoft visual studio 10.0\vc\include\ostream(427): or       'std::basic_ostream<_Elem,_Traits> &std::basic_ostream<_Elem,_Traits>::operator <<(double)'
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]
1>          c:\program files\microsoft visual studio 10.0\vc\include\ostream(447): or       'std::basic_ostream<_Elem,_Traits> &std::basic_ostream<_Elem,_Traits>::operator <<(long double)'
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]
1>          c:\program files\microsoft visual studio 10.0\vc\include\ostream(467): or       'std::basic_ostream<_Elem,_Traits> &std::basic_ostream<_Elem,_Traits>::operator <<(const void *)'
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]
1>          c:\program files\microsoft visual studio 10.0\vc\include\ostream(487): or       'std::basic_ostream<_Elem,_Traits> &std::basic_ostream<_Elem,_Traits>::operator <<(std::basic_streambuf<_Elem,_Traits> *)'
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]
1>          while trying to match the argument list '(std::basic_ostream<_Elem,_Traits>, const T1)'
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]
1>          c:\boost_1_49_0\boost\variant\variant.hpp(858) : see reference to function template instantiation 'void boost::detail::variant::printer<OStream>::operator ()<const T>(const T &) const' being compiled
1>          with
1>          [
1>              OStream=std::basic_ostream<char,std::char_traits<char>>,
1>              T=T1
1>          ]
1>          c:\boost_1_49_0\boost\variant\detail\visitation_impl.hpp(145) : see reference to function template instantiation 'void boost::detail::variant::invoke_visitor<Visitor>::internal_visit<const T>(T &,int)' being compiled
1>          with
1>          [
1>              Visitor=boost::detail::variant::printer<std::basic_ostream<char,std::char_traits<char>>>,
1>              T=T1
1>          ]
1>          c:\boost_1_49_0\boost\variant\detail\visitation_impl.hpp(173) : see reference to function template instantiation 'void boost::detail::variant::visitation_impl_invoke_impl<Visitor,VoidPtrCV,T>(int,Visitor &,VoidPtrCV,T *,boost::mpl::false_)' being compiled
1>          with
1>          [
1>              Visitor=boost::detail::variant::invoke_visitor<boost::detail::variant::printer<std::basic_ostream<char,std::char_traits<char>>>>,
1>              VoidPtrCV=const void *,
1>              T=T1
1>          ]
1>          c:\boost_1_49_0\boost\variant\detail\visitation_impl.hpp(256) : see reference to function template instantiation 'void boost::detail::variant::visitation_impl_invoke<Visitor,VoidPtrCV,T1,NoBackupFlag>(int,Visitor &,VoidPtrCV,T *,NoBackupFlag,int)' being compiled
1>          with
1>          [
1>              Visitor=boost::detail::variant::invoke_visitor<boost::detail::variant::printer<std::basic_ostream<char,std::char_traits<char>>>>,
1>              VoidPtrCV=const void *,
1>              NoBackupFlag=boost::variant<std::vector<testing::internal::string>,std::vector<int8_t>>::has_fallback_type_,
1>              T=T1
1>          ]
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1 Answer

  1. Editorial Team
    EXPECT_EQ(c1==c2);

    This fails, because it expects two argument (see this).

    You could use EXPECT_TRUE(condition); if it suits your need :

    EXPECT_TRUE(c1==c2);

    EDIT:

    See this :

    We used to require the arguments to support the << operator for streaming to an ostream, but it’s no longer necessary since v1.6.0 (if << is supported, it will be called to print the arguments when the assertion fails; otherwise Google Test will attempt to print them in the best way it can.

    Therefore, unless the version you use is not 1.6.0, or greater, you need to have operator<< defined.

    • 0