clang++ с флагом C++11 показывает, что ссылка на значение не может быть привязана к ошибке lvalue
Я написал простую программу на C++ t.cpp:
// t.cpp
#include <vector>
#include <string>
using namespace std;
int main() {
vector<string> strVec;
string a("a");
strVec.push_back(a);
return 0;
}
Затем я скомпилировал его с помощью clang++ 3.4 на CentOS 6.5 x64. Он может быть скомпилирован без каких-либо ошибок с помощью этой команды:
clang++ t.cpp
Однако, если я включил флаг C++11, -std= C++11:
clang++ -std=c++11 t.cpp
Я получил много сообщений об ошибках:
In file included from t.cpp:1:
In file included from /usr/bin/../lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/vector:61:
In file included from /usr/bin/../lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/bits/stl_algobase.h:66:
In file included from /usr/bin/../lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/bits/stl_pair.h:60:
/usr/bin/../lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/bits/move.h:57:14: error: rvalue reference to type 'basic_string<[3 * ...]>' cannot bind to lvalue of type
'basic_string<[3 * ...]>'
{ return __t; }
^~~
/usr/bin/../lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/bits/vector.tcc:302:7: note: in instantiation of function template specialization
'std::move<std::basic_string<char> &>' requested here
_GLIBCXX_MOVE(*(this->_M_impl._M_finish
^
/usr/bin/../lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/bits/move.h:61:33: note: expanded from macro '_GLIBCXX_MOVE'
#define _GLIBCXX_MOVE(_Tp) std::move(_Tp)
^
/usr/bin/../lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/bits/stl_vector.h:741:4: note: in instantiation of function template specialization
'std::vector<std::basic_string<char>, std::allocator<std::basic_string<char> > >::_M_insert_aux<const std::basic_string<char> &>' requested here
_M_insert_aux(end(), __x);
^
t.cpp:8:9: note: in instantiation of member function 'std::vector<std::basic_string<char>, std::allocator<std::basic_string<char> > >::push_back' requested here
strVec.push_back(a);
^
In file included from t.cpp:1:
In file included from /usr/bin/../lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/vector:62:
In file included from /usr/bin/../lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/bits/allocator.h:48:
In file included from /usr/bin/../lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/x86_64-redhat-linux/bits/c++allocator.h:34:
/usr/bin/../lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/ext/new_allocator.h:111:27: error: no matching function for call to 'forward'
{ ::new((void *)__p) _Tp(std::forward<_Args>(__args)...); }
^~~~~~~~~~~~~~~~~~~
/usr/bin/../lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/bits/vector.tcc:301:18: note: in instantiation of function template specialization
'__gnu_cxx::new_allocator<std::basic_string<char> >::construct<std::basic_string<char> >' requested here
this->_M_impl.construct(this->_M_impl._M_finish,
^
/usr/bin/../lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/bits/stl_vector.h:741:4: note: in instantiation of function template specialization
'std::vector<std::basic_string<char>, std::allocator<std::basic_string<char> > >::_M_insert_aux<const std::basic_string<char> &>' requested here
_M_insert_aux(end(), __x);
^
t.cpp:8:9: note: in instantiation of member function 'std::vector<std::basic_string<char>, std::allocator<std::basic_string<char> > >::push_back' requested here
strVec.push_back(a);
^
/usr/bin/../lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/bits/move.h:51:5: note: candidate function [with _Tp = std::basic_string<char>] not viable: no known conversion
from 'std::basic_string<char>' to 'typename std::identity<basic_string<char> >::type &&' (aka 'std::basic_string<char> &&') for 1st argument
forward(typename std::identity<_Tp>::type&& __t)
^
In file included from t.cpp:1:
In file included from /usr/bin/../lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/vector:61:
/usr/bin/../lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/bits/stl_algobase.h:561:20: error: no matching function for call to 'move'
*--__result = std::move(*--__last);
^~~~~~~~~
/usr/bin/../lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/bits/stl_algobase.h:593:45: note: in instantiation of function template specialization
'std::__copy_move_backward<true, false, std::random_access_iterator_tag>::__copy_move_b<std::basic_string<char> *, std::basic_string<char> *>' requested here
_Category>::__copy_move_b(__first,
^
/usr/bin/../lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/bits/stl_algobase.h:602:24: note: in instantiation of function template specialization
'std::__copy_move_backward_a<true, std::basic_string<char> *, std::basic_string<char> *>' requested here
return _BI2(std::__copy_move_backward_a<_IsMove>
^
/usr/bin/../lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/bits/stl_algobase.h:674:20: note: in instantiation of function template specialization
'std::__copy_move_backward_a2<true, std::basic_string<char> *, std::basic_string<char> *>' requested here
return (std::__copy_move_backward_a2<true>
^
/usr/bin/../lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/bits/vector.tcc:308:4: note: in instantiation of function template specialization
'std::move_backward<std::basic_string<char> *, std::basic_string<char> *>' requested here
_GLIBCXX_MOVE_BACKWARD3(__position.base(),
^
/usr/bin/../lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/bits/stl_algobase.h:679:53: note: expanded from macro '_GLIBCXX_MOVE_BACKWARD3'
#define _GLIBCXX_MOVE_BACKWARD3(_Tp, _Up, _Vp) std::move_backward(_Tp, _Up, _Vp)
^
/usr/bin/../lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/bits/stl_vector.h:741:4: note: in instantiation of function template specialization
'std::vector<std::basic_string<char>, std::allocator<std::basic_string<char> > >::_M_insert_aux<const std::basic_string<char> &>' requested here
_M_insert_aux(end(), __x);
^
t.cpp:8:9: note: in instantiation of member function 'std::vector<std::basic_string<char>, std::allocator<std::basic_string<char> > >::push_back' requested here
strVec.push_back(a);
^
/usr/bin/../lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/bits/move.h:56:5: note: candidate template ignored: substitution failure [with _Tp = std::basic_string<char> &]
move(_Tp&& __t)
^
/usr/bin/../lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/bits/stl_algobase.h:491:5: note: candidate function template not viable: requires 3 arguments, but 1 was provided
move(_II __first, _II __last, _OI __result)
^
In file included from t.cpp:1:
In file included from /usr/bin/../lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/vector:61:
In file included from /usr/bin/../lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/bits/stl_algobase.h:69:
/usr/bin/../lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/bits/stl_iterator.h:916:16: error: rvalue reference to type 'basic_string<[3 * ...]>' cannot bind to lvalue of
type 'basic_string<[3 * ...]>'
{ return *_M_current; }
^~~~~~~~~~~
/usr/bin/../lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/bits/stl_uninitialized.h:74:28: note: in instantiation of member function
'std::move_iterator<std::basic_string<char> *>::operator*' requested here
std::_Construct(&*__cur, *__first);
^
/usr/bin/../lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/bits/stl_uninitialized.h:116:2: note: in instantiation of function template specialization
'std::__uninitialized_copy<false>::uninitialized_copy<std::move_iterator<std::basic_string<char> *>, std::basic_string<char> *>' requested here
uninitialized_copy(__first, __last, __result);
^
/usr/bin/../lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/bits/stl_uninitialized.h:256:19: note: in instantiation of function template specialization
'std::uninitialized_copy<std::move_iterator<std::basic_string<char> *>, std::basic_string<char> *>' requested here
{ return std::uninitialized_copy(__first, __last, __result); }
^
/usr/bin/../lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/bits/stl_uninitialized.h:264:19: note: in instantiation of function template specialization
'std::__uninitialized_copy_a<std::move_iterator<std::basic_string<char> *>, std::basic_string<char> *, std::basic_string<char> >' requested here
return std::__uninitialized_copy_a(_GLIBCXX_MAKE_MOVE_ITERATOR(__first),
^
/usr/bin/../lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/bits/vector.tcc:339:8: note: in instantiation of function template specialization
'std::__uninitialized_move_a<std::basic_string<char> *, std::basic_string<char> *, std::allocator<std::basic_string<char> > >' requested here
std::__uninitialized_move_a(this->_M_impl._M_start,
^
/usr/bin/../lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/bits/stl_vector.h:741:4: note: in instantiation of function template specialization
'std::vector<std::basic_string<char>, std::allocator<std::basic_string<char> > >::_M_insert_aux<const std::basic_string<char> &>' requested here
_M_insert_aux(end(), __x);
^
t.cpp:8:9: note: in instantiation of member function 'std::vector<std::basic_string<char>, std::allocator<std::basic_string<char> > >::push_back' requested here
strVec.push_back(a);
^
In file included from t.cpp:1:
In file included from /usr/bin/../lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/vector:63:
/usr/bin/../lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/bits/stl_construct.h:73:42: error: no matching function for call to 'forward'
::new(static_cast<void*>(__p)) _T1(std::forward<_T2>(__value));
^~~~~~~~~~~~~~~~~
/usr/bin/../lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/bits/stl_uninitialized.h:74:8: note: in instantiation of function template specialization
'std::_Construct<std::basic_string<char>, std::basic_string<char> >' requested here
std::_Construct(&*__cur, *__first);
^
/usr/bin/../lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/bits/stl_uninitialized.h:116:2: note: in instantiation of function template specialization
'std::__uninitialized_copy<false>::uninitialized_copy<std::move_iterator<std::basic_string<char> *>, std::basic_string<char> *>' requested here
uninitialized_copy(__first, __last, __result);
^
/usr/bin/../lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/bits/stl_uninitialized.h:256:19: note: in instantiation of function template specialization
'std::uninitialized_copy<std::move_iterator<std::basic_string<char> *>, std::basic_string<char> *>' requested here
{ return std::uninitialized_copy(__first, __last, __result); }
^
/usr/bin/../lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/bits/stl_uninitialized.h:264:19: note: in instantiation of function template specialization
'std::__uninitialized_copy_a<std::move_iterator<std::basic_string<char> *>, std::basic_string<char> *, std::basic_string<char> >' requested here
return std::__uninitialized_copy_a(_GLIBCXX_MAKE_MOVE_ITERATOR(__first),
^
/usr/bin/../lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/bits/vector.tcc:339:8: note: in instantiation of function template specialization
'std::__uninitialized_move_a<std::basic_string<char> *, std::basic_string<char> *, std::allocator<std::basic_string<char> > >' requested here
std::__uninitialized_move_a(this->_M_impl._M_start,
^
/usr/bin/../lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/bits/stl_vector.h:741:4: note: in instantiation of function template specialization
'std::vector<std::basic_string<char>, std::allocator<std::basic_string<char> > >::_M_insert_aux<const std::basic_string<char> &>' requested here
_M_insert_aux(end(), __x);
^
t.cpp:8:9: note: in instantiation of member function 'std::vector<std::basic_string<char>, std::allocator<std::basic_string<char> > >::push_back' requested here
strVec.push_back(a);
^
/usr/bin/../lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/bits/move.h:51:5: note: candidate function [with _Tp = std::basic_string<char>] not viable: no known conversion
from 'std::basic_string<char>' to 'typename std::identity<basic_string<char> >::type &&' (aka 'std::basic_string<char> &&') for 1st argument
forward(typename std::identity<_Tp>::type&& __t)
^
5 errors generated.
Одна ошибка:
error: rvalue reference to type 'basic_string<[3 * ...]>' cannot bind to lvalue of type
'basic_string<[3 * ...]>'
Что это значит?
1 ответ
Решение
Ваш код в порядке. Проблема в том, что вы используете слишком старую версию libstdC++. Либо обновите его, либо используйте libC++, если он у вас установлен (добавьте -stdlib=libc++ на ваш вызов Clang++).