/in/foo.cc: In function 'int main()':
/in/foo.cc:22:13: error: no match for 'operator+' (operand types are 'std::__cxx11::string {aka std::__cxx11::basic_string<char>}' and 'std::vector<std::__cxx11::basic_string<char> >')
   str = str + vec;
         ~~~~^~~~~
In file included from /usr/include/c++/6/vector:65:0,
                 from /in/foo.cc:13:
/usr/include/c++/6/bits/stl_bvector.h:387:3: note: candidate: std::_Bit_const_iterator std::operator+(std::ptrdiff_t, const std::_Bit_const_iterator&)
   operator+(ptrdiff_t __n, const _Bit_const_iterator& __x)
   ^~~~~~~~
/usr/include/c++/6/bits/stl_bvector.h:387:3: note:   no known conversion for argument 1 from 'std::__cxx11::string {aka std::__cxx11::basic_string<char>}' to 'std::ptrdiff_t {aka long int}'
/usr/include/c++/6/bits/stl_bvector.h:297:3: note: candidate: std::_Bit_iterator std::operator+(std::ptrdiff_t, const std::_Bit_iterator&)
   operator+(ptrdiff_t __n, const _Bit_iterator& __x)
   ^~~~~~~~
/usr/include/c++/6/bits/stl_bvector.h:297:3: note:   no known conversion for argument 1 from 'std::__cxx11::string {aka std::__cxx11::basic_string<char>}' to 'std::ptrdiff_t {aka long int}'
In file included from /usr/include/c++/6/string:52:0,
                 from /usr/include/c++/6/bits/locale_classes.h:40,
                 from /usr/include/c++/6/bits/ios_base.h:41,
                 from /usr/include/c++/6/ios:42,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from /in/foo.cc:11:
/usr/include/c++/6/bits/basic_string.h:5051:5: note: candidate: template<class _CharT, class _Traits, class _Alloc> std::__cxx11::basic_string<_CharT, _Traits, _Alloc> std::operator+(std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&&, _CharT)
     operator+(basic_string<_CharT, _Traits, _Alloc>&& __lhs,
     ^~~~~~~~
/usr/include/c++/6/bits/basic_string.h:5051:5: note:   template argument deduction/substitution failed:
/in/foo.cc:22:15: note:   deduced conflicting types for parameter '_CharT' ('char' and 'std::vector<std::__cxx11::basic_string<char> >')
   str = str + vec;
               ^~~
In file included from /usr/include/c++/6/string:52:0,
                 from /usr/include/c++/6/bits/locale_classes.h:40,
                 from /usr/include/c++/6/bits/ios_base.h:41,
                 from /usr/include/c++/6/ios:42,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from /in/foo.cc:11:
/usr/include/c++/6/bits/basic_string.h:5045:5: note: candidate: template<class _CharT, class _Traits, class _Alloc> std::__cxx11::basic_string<_CharT, _Traits, _Alloc> std::operator+(std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&&, const _CharT*)
     operator+(basic_string<_CharT, _Traits, _Alloc>&& __lhs,
     ^~~~~~~~
/usr/include/c++/6/bits/basic_string.h:5045:5: note:   template argument deduction/substitution failed:
/in/foo.cc:22:15: note:   mismatched types 'const _CharT*' and 'std::vector<std::__cxx11::basic_string<char> >'
   str = str + vec;
               ^~~
In file included from /usr/include/c++/6/string:52:0,
                 from /usr/include/c++/6/bits/locale_classes.h:40,
                 from /usr/include/c++/6/bits/ios_base.h:41,
                 from /usr/include/c++/6/ios:42,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from /in/foo.cc:11:
/usr/include/c++/6/bits/basic_string.h:5039:5: note: candidate: template<class _CharT, class _Traits, class _Alloc> std::__cxx11::basic_string<_CharT, _Traits, _Alloc> std::operator+(_CharT, std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&&)
     operator+(_CharT __lhs,
     ^~~~~~~~
/usr/include/c++/6/bits/basic_string.h:5039:5: note:   template argument deduction/substitution failed:
/in/foo.cc:22:15: note:   'std::vector<std::__cxx11::basic_string<char> >' is not derived from 'std::__cxx11::basic_string<_CharT, _Traits, _Alloc>'
   str = str + vec;
               ^~~
In file included from /usr/include/c++/6/string:52:0,
                 from /usr/include/c++/6/bits/locale_classes.h:40,
                 from /usr/include/c++/6/bits/ios_base.h:41,
                 from /usr/include/c++/6/ios:42,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from /in/foo.cc:11:
/usr/include/c++/6/bits/basic_string.h:5033:5: note: candidate: template<class _CharT, class _Traits, class _Alloc> std::__cxx11::basic_string<_CharT, _Traits, _Alloc> std::operator+(const _CharT*, std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&&)
     operator+(const _CharT* __lhs,
     ^~~~~~~~
/usr/include/c++/6/bits/basic_string.h:5033:5: note:   template argument deduction/substitution failed:
/in/foo.cc:22:15: note:   mismatched types 'const _CharT*' and 'std::__cxx11::basic_string<char>'
   str = str + vec;
               ^~~
In file included from /usr/include/c++/6/string:52:0,
                 from /usr/include/c++/6/bits/locale_classes.h:40,
                 from /usr/include/c++/6/bits/ios_base.h:41,
                 from /usr/include/c++/6/ios:42,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from /in/foo.cc:11:
/usr/include/c++/6/bits/basic_string.h:5021:5: note: candidate: template<class _CharT, class _Traits, class _Alloc> std::__cxx11::basic_string<_CharT, _Traits, _Alloc> std::operator+(std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&&, std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&&)
     operator+(basic_string<_CharT, _Traits, _Alloc>&& __lhs,
     ^~~~~~~~
/usr/include/c++/6/bits/basic_string.h:5021:5: note:   template argument deduction/substitution failed:
/in/foo.cc:22:15: note:   'std::vector<std::__cxx11::basic_string<char> >' is not derived from 'std::__cxx11::basic_string<_CharT, _Traits, _Alloc>'
   str = str + vec;
               ^~~
In file included from /usr/include/c++/6/string:52:0,
                 from /usr/include/c++/6/bits/locale_classes.h:40,
                 from /usr/include/c++/6/bits/ios_base.h:41,
                 from /usr/include/c++/6/ios:42,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from /in/foo.cc:11:
/usr/include/c++/6/bits/basic_string.h:5015:5: note: candidate: template<class _CharT, class _Traits, class _Alloc> std::__cxx11::basic_string<_CharT, _Traits, _Alloc> std::operator+(const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&, std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&&)
     operator+(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
     ^~~~~~~~
/usr/include/c++/6/bits/basic_string.h:5015:5: note:   template argument deduction/substitution failed:
/in/foo.cc:22:15: note:   'std::vector<std::__cxx11::basic_string<char> >' is not derived from 'std::__cxx11::basic_string<_CharT, _Traits, _Alloc>'
   str = str + vec;
               ^~~
In file included from /usr/include/c++/6/string:52:0,
                 from /usr/include/c++/6/bits/locale_classes.h:40,
                 from /usr/include/c++/6/bits/ios_base.h:41,
                 from /usr/include/c++/6/ios:42,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from /in/foo.cc:11:
/usr/include/c++/6/bits/basic_string.h:5009:5: note: candidate: template<class _CharT, class _Traits, class _Alloc> std::__cxx11::basic_string<_CharT, _Traits, _Alloc> std::operator+(std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&&, const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&)
     operator+(basic_string<_CharT, _Traits, _Alloc>&& __lhs,
     ^~~~~~~~
/usr/include/c++/6/bits/basic_string.h:5009:5: note:   template argument deduction/substitution failed:
/in/foo.cc:22:15: note:   'std::vector<std::__cxx11::basic_string<char> >' is not derived from 'const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>'
   str = str + vec;
               ^~~
In file included from /usr/include/c++/6/string:52:0,
                 from /usr/in