我正在尝试执行以下操作：
#include <memory>
#include <vector>
#include <queue>
int main() {
std::vector<std::queue<std::unique_ptr<int>>> v;
v.resize(10);
}
但我在GCC 10.2中得到了这个：
$ g++ test.cpp -o test
In file included from /usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/include/g++-v10/memory:66,
from test.cpp:1:
/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/include/g++-v10/bits/stl_uninitialized.h: In instantiation of '_ForwardIterator std::uninitialized_copy(_InputIterator, _InputIterator, _ForwardIterator) [with _InputIterator = std::_Deque_iterator<std::unique_ptr<int>, const std::unique_ptr<int>&, const std::unique_ptr<int>*>; _ForwardIterator = std::_Deque_iterator<std::unique_ptr<int>, std::unique_ptr<int>&, std::unique_ptr<int>*>]':
/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/include/g++-v10/bits/stl_uninitialized.h:325:37: required from '_ForwardIterator std::__uninitialized_copy_a(_InputIterator, _InputIterator, _ForwardIterator, std::allocator<_Tp>&) [with _InputIterator = std::_Deque_iterator<std::unique_ptr<int>, const std::unique_ptr<int>&, const std::unique_ptr<int>*>; _ForwardIterator = std::_Deque_iterator<std::unique_ptr<int>, std::unique_ptr<int>&, std::unique_ptr<int>*>; _Tp = std::unique_ptr<int>]'
/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/include/g++-v10/bits/stl_deque.h:896:36: required from 'std::deque<_Tp, _Alloc>::deque(const std::deque<_Tp, _Alloc>&) [with _Tp = std::unique_ptr<int>; _Alloc = std::allocator<std::unique_ptr<int> >]'
/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/include/g++-v10/bits/stl_queue.h:96:11: required from 'void std::_Construct(_Tp*, _Args&& ...) [with _Tp = std::queue<std::unique_ptr<int> >; _Args = {const std::queue<std::unique_ptr<int, std::default_delete<int> >, std::deque<std::unique_ptr<int, std::default_delete<int> >, std::allocator<std::unique_ptr<int, std::default_delete<int> > > > >&}]'
/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/include/g++-v10/bits/stl_uninitialized.h:91:18: required from 'static _ForwardIterator std::__uninitialized_copy<_TrivialValueTypes>::__uninit_copy(_InputIterator, _InputIterator, _ForwardIterator) [with _InputIterator = const std::queue<std::unique_ptr<int> >*; _ForwardIterator = std::queue<std::unique_ptr<int> >*; bool _TrivialValueTypes = false]'
/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/include/g++-v10/bits/stl_uninitialized.h:150:15: required from '_ForwardIterator std::uninitialized_copy(_InputIterator, _InputIterator, _ForwardIterator) [with _InputIterator = const std::queue<std::unique_ptr<int> >*; _ForwardIterator = std::queue<std::unique_ptr<int> >*]'
/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/include/g++-v10/bits/stl_uninitialized.h:325:37: required from '_ForwardIterator std::__uninitialized_copy_a(_InputIterator, _InputIterator, _ForwardIterator, std::allocator<_Tp>&) [with _InputIterator = const std::queue<std::unique_ptr<int> >*; _ForwardIterator = std::queue<std::unique_ptr<int> >*; _Tp = std::queue<std::unique_ptr<int> >]'
/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/include/g++-v10/bits/stl_uninitialized.h:347:2: required from '_ForwardIterator std::__uninitialized_move_if_noexcept_a(_InputIterator, _InputIterator, _ForwardIterator, _Allocator&) [with _InputIterator = std::queue<std::unique_ptr<int> >*; _ForwardIterator = std::queue<std::unique_ptr<int> >*; _Allocator = std::allocator<std::queue<std::unique_ptr<int> > >]'
/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/include/g++-v10/bits/vector.tcc:659:48: required from 'void std::vector<_Tp, _Alloc>::_M_default_append(std::vector<_Tp, _Alloc>::size_type) [with _Tp = std::queue<std::unique_ptr<int> >; _Alloc = std::allocator<std::queue<std::unique_ptr<int> > >; std::vector<_Tp, _Alloc>::size_type = long unsigned int]'
/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/include/g++-v10/bits/stl_vector.h:940:4: required from 'void std::vector<_Tp, _Alloc>::resize(std::vector<_Tp, _Alloc>::size_type) [with _Tp = std::queue<std::unique_ptr<int> >; _Alloc = std::allocator<std::queue<std::unique_ptr<int> > >; std::vector<_Tp, _Alloc>::size_type = long unsigned int]'
test.cpp:7:16: required from here
/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/include/g++-v10/bits/stl_uninitialized.h:137:72: error: static assertion failed: result type must be constructible from value type of input range
137 | static_assert(is_constructible<_ValueType2, decltype(*__first)>::value,
| ^~~~~
与clang++11:相同
$ clang++-11 test.cpp -o test
In file included from test.cpp:1:
In file included from /usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/include/g++-v10/memory:66:
/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/include/g++-v10/bits/stl_uninitialized.h:137:7: error: static_assert failed due to requirement 'is_constructible<std::unique_ptr<int, std::default_delete<int>>, const std::unique_ptr<int, std::default_delete<int>> &>::value' "result type must be constructible from value type of input range"
static_assert(is_constructible<_ValueType2, decltype(*__first)>::value,
^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/include/g++-v10/bits/stl_uninitialized.h:325:19: note: in instantiation of function template specialization 'std::uninitialized_copy<std::_Deque_iterator<std::unique_ptr<int, std::default_delete<int>>, const std::unique_ptr<int, std::default_delete<int>> &, const std::unique_ptr<int, std::default_delete<int>> *>, std::_Deque_iterator<std::unique_ptr<int, std::default_delete<int>>, std::unique_ptr<int, std::default_delete<int>> &, std::unique_ptr<int, std::default_delete<int>> *>>' requested here
{ return std::uninitialized_copy(__first, __last, __result); }
^
/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/include/g++-v10/bits/stl_deque.h:896:14: note: in instantiation of function template specialization 'std::__uninitialized_copy_a<std::_Deque_iterator<std::unique_ptr<int, std::default_delete<int>>, const std::unique_ptr<int, std::default_delete<int>> &, const std::unique_ptr<int, std::default_delete<int>> *>, std::_Deque_iterator<std::unique_ptr<int, std::default_delete<int>>, std::unique_ptr<int, std::default_delete<int>> &, std::unique_ptr<int, std::default_delete<int>> *>, std::unique_ptr<int, std::default_delete<int>>>' requested here
{ std::__uninitialized_copy_a(__x.begin(), __x.end(),
^
/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/include/g++-v10/bits/stl_queue.h:96:11: note: in instantiation of member function 'std::deque<std::unique_ptr<int, std::default_delete<int>>, std::allocator<std::unique_ptr<int, std::default_delete<int>>>>::deque' requested here
class queue
^
/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/include/g++-v10/bits/stl_uninitialized.h:91:8: note: in instantiation of function template specialization 'std::_Construct<std::queue<std::unique_ptr<int, std::default_delete<int>>, std::deque<std::unique_ptr<int, std::default_delete<int>>, std::allocator<std::unique_ptr<int, std::default_delete<int>>>>>, const std::queue<std::unique_ptr<int, std::default_delete<int>>, std::deque<std::unique_ptr<int, std::default_delete<int>>, std::allocator<std::unique_ptr<int, std::default_delete<int>>>>> &>' requested here
std::_Construct(std::__addressof(*__cur), *__first);
^
/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/include/g++-v10/bits/stl_uninitialized.h:150:2: note: in instantiation of function template specialization 'std::__uninitialized_copy<false>::__uninit_copy<const std::queue<std::unique_ptr<int, std::default_delete<int>>, std::deque<std::unique_ptr<int, std::default_delete<int>>, std::allocator<std::unique_ptr<int, std::default_delete<int>>>>> *, std::queue<std::unique_ptr<int, std::default_delete<int>>, std::deque<std::unique_ptr<int, std::default_delete<int>>, std::allocator<std::unique_ptr<int, std::default_delete<int>>>>> *>' requested here
__uninit_copy(__first, __last, __result);
^
/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/include/g++-v10/bits/stl_uninitialized.h:325:19: note: in instantiation of function template specialization 'std::uninitialized_copy<const std::queue<std::unique_ptr<int, std::default_delete<int>>, std::deque<std::unique_ptr<int, std::default_delete<int>>, std::allocator<std::unique_ptr<int, std::default_delete<int>>>>> *, std::queue<std::unique_ptr<int, std::default_delete<int>>, std::deque<std::unique_ptr<int, std::default_delete<int>>, std::allocator<std::unique_ptr<int, std::default_delete<int>>>>> *>' requested here
{ return std::uninitialized_copy(__first, __last, __result); }
^
/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/include/g++-v10/bits/stl_uninitialized.h:346:19: note: in instantiation of function template specialization 'std::__uninitialized_copy_a<const std::queue<std::unique_ptr<int, std::default_delete<int>>, std::deque<std::unique_ptr<int, std::default_delete<int>>, std::allocator<std::unique_ptr<int, std::default_delete<int>>>>> *, std::queue<std::unique_ptr<int, std::default_delete<int>>, std::deque<std::unique_ptr<int, std::default_delete<int>>, std::allocator<std::unique_ptr<int, std::default_delete<int>>>>> *, std::queue<std::unique_ptr<int, std::default_delete<int>>, std::deque<std::unique_ptr<int, std::default_delete<int>>, std::allocator<std::unique_ptr<int, std::default_delete<int>>>>>>' requested here
return std::__uninitialized_copy_a
^
/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/include/g++-v10/bits/vector.tcc:659:14: note: in instantiation of function template specialization 'std::__uninitialized_move_if_noexcept_a<std::queue<std::unique_ptr<int, std::default_delete<int>>, std::deque<std::unique_ptr<int, std::default_delete<int>>, std::allocator<std::unique_ptr<int, std::default_delete<int>>>>> *, std::queue<std::unique_ptr<int, std::default_delete<int>>, std::deque<std::unique_ptr<int, std::default_delete<int>>, std::allocator<std::unique_ptr<int, std::default_delete<int>>>>> *, std::allocator<std::queue<std::unique_ptr<int, std::default_delete<int>>, std::deque<std::unique_ptr<int, std::default_delete<int>>, std::allocator<std::unique_ptr<int, std::default_delete<int>>>>>>>' requested here
std::__uninitialized_move_if_noexcept_a(
^
/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/include/g++-v10/bits/stl_vector.h:940:4: note: in instantiation of member function 'std::vector<std::queue<std::unique_ptr<int, std::default_delete<int>>, std::deque<std::unique_ptr<int, std::default_delete<int>>, std::allocator<std::unique_ptr<int, std::default_delete<int>>>>>, std::allocator<std::queue<std::unique_ptr<int, std::default_delete<int>>, std::deque<std::unique_ptr<int, std::default_delete<int>>, std::allocator<std::unique_ptr<int, std::default_delete<int>>>>>>>::_M_default_append' requested here
_M_default_append(__new_size - size());
^
test.cpp:7:7: note: in instantiation of member function 'std::vector<std::queue<std::unique_ptr<int, std::default_delete<int>>, std::deque<std::unique_ptr<int, std::default_delete<int>>, std::allocator<std::unique_ptr<int, std::default_delete<int>>>>>, std::allocator<std::queue<std::unique_ptr<int, std::default_delete<int>>, std::deque<std::unique_ptr<int, std::default_delete<int>>, std::allocator<std::unique_ptr<int, std::default_delete<int>>>>>>>::resize' requested here
v.resize(10);
^
In file included from test.cpp:1:
In file included from /usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/include/g++-v10/memory:65:
/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/include/g++-v10/bits/stl_construct.h:109:38: error: call to deleted constructor of 'std::unique_ptr<int, std::default_delete<int>>'
{ ::new(static_cast<void*>(__p)) _Tp(std::forward<_Args>(__args)...); }
^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/include/g++-v10/bits/stl_uninitialized.h:91:8: note: in instantiation of function template specialization 'std::_Construct<std::unique_ptr<int, std::default_delete<int>>, const std::unique_ptr<int, std::default_delete<int>> &>' requested here
std::_Construct(std::__addressof(*__cur), *__first);
^
/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/include/g++-v10/bits/stl_uninitialized.h:150:2: note: in instantiation of function template specialization 'std::__uninitialized_copy<false>::__uninit_copy<std::_Deque_iterator<std::unique_ptr<int, std::default_delete<int>>, const std::unique_ptr<int, std::default_delete<int>> &, const std::unique_ptr<int, std::default_delete<int>> *>, std::_Deque_iterator<std::unique_ptr<int, std::default_delete<int>>, std::unique_ptr<int, std::default_delete<int>> &, std::unique_ptr<int, std::default_delete<int>> *>>' requested here
__uninit_copy(__first, __last, __result);
^
/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/include/g++-v10/bits/stl_uninitialized.h:325:19: note: in instantiation of function template specialization 'std::uninitialized_copy<std::_Deque_iterator<std::unique_ptr<int, std::default_delete<int>>, const std::unique_ptr<int, std::default_delete<int>> &, const std::unique_ptr<int, std::default_delete<int>> *>, std::_Deque_iterator<std::unique_ptr<int, std::default_delete<int>>, std::unique_ptr<int, std::default_delete<int>> &, std::unique_ptr<int, std::default_delete<int>> *>>' requested here
{ return std::uninitialized_copy(__first, __last, __result); }
^
/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/include/g++-v10/bits/stl_deque.h:896:14: note: in instantiation of function template specialization 'std::__uninitialized_copy_a<std::_Deque_iterator<std::unique_ptr<int, std::default_delete<int>>, const std::unique_ptr<int, std::default_delete<int>> &, const std::unique_ptr<int, std::default_delete<int>> *>, std::_Deque_iterator<std::unique_ptr<int, std::default_delete<int>>, std::unique_ptr<int, std::default_delete<int>> &, std::unique_ptr<int, std::default_delete<int>> *>, std::unique_ptr<int, std::default_delete<int>>>' requested here
{ std::__uninitialized_copy_a(__x.begin(), __x.end(),
^
/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/include/g++-v10/bits/stl_queue.h:96:11: note: in instantiation of member function 'std::deque<std::unique_ptr<int, std::default_delete<int>>, std::allocator<std::unique_ptr<int, std::default_delete<int>>>>::deque' requested here
class queue
^
/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/include/g++-v10/bits/stl_uninitialized.h:91:8: note: (skipping 2 contexts in backtrace; use -ftemplate-backtrace-limit=0 to see all)
std::_Construct(std::__addressof(*__cur), *__first);
^
/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/include/g++-v10/bits/stl_uninitialized.h:325:19: note: in instantiation of function template specialization 'std::uninitialized_copy<const std::queue<std::unique_ptr<int, std::default_delete<int>>, std::deque<std::unique_ptr<int, std::default_delete<int>>, std::allocator<std::unique_ptr<int, std::default_delete<int>>>>> *, std::queue<std::unique_ptr<int, std::default_delete<int>>, std::deque<std::unique_ptr<int, std::default_delete<int>>, std::allocator<std::unique_ptr<int, std::default_delete<int>>>>> *>' requested here
{ return std::uninitialized_copy(__first, __last, __result); }
^
/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/include/g++-v10/bits/stl_uninitialized.h:346:19: note: in instantiation of function template specialization 'std::__uninitialized_copy_a<const std::queue<std::unique_ptr<int, std::default_delete<int>>, std::deque<std::unique_ptr<int, std::default_delete<int>>, std::allocator<std::unique_ptr<int, std::default_delete<int>>>>> *, std::queue<std::unique_ptr<int, std::default_delete<int>>, std::deque<std::unique_ptr<int, std::default_delete<int>>, std::allocator<std::unique_ptr<int, std::default_delete<int>>>>> *, std::queue<std::unique_ptr<int, std::default_delete<int>>, std::deque<std::unique_ptr<int, std::default_delete<int>>, std::allocator<std::unique_ptr<int, std::default_delete<int>>>>>>' requested here
return std::__uninitialized_copy_a
^
/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/include/g++-v10/bits/vector.tcc:659:14: note: in instantiation of function template specialization 'std::__uninitialized_move_if_noexcept_a<std::queue<std::unique_ptr<int, std::default_delete<int>>, std::deque<std::unique_ptr<int, std::default_delete<int>>, std::allocator<std::unique_ptr<int, std::default_delete<int>>>>> *, std::queue<std::unique_ptr<int, std::default_delete<int>>, std::deque<std::unique_ptr<int, std::default_delete<int>>, std::allocator<std::unique_ptr<int, std::default_delete<int>>>>> *, std::allocator<std::queue<std::unique_ptr<int, std::default_delete<int>>, std::deque<std::unique_ptr<int, std::default_delete<int>>, std::allocator<std::unique_ptr<int, std::default_delete<int>>>>>>>' requested here
std::__uninitialized_move_if_noexcept_a(
^
/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/include/g++-v10/bits/stl_vector.h:940:4: note: in instantiation of member function 'std::vector<std::queue<std::unique_ptr<int, std::default_delete<int>>, std::deque<std::unique_ptr<int, std::default_delete<int>>, std::allocator<std::unique_ptr<int, std::default_delete<int>>>>>, std::allocator<std::queue<std::unique_ptr<int, std::default_delete<int>>, std::deque<std::unique_ptr<int, std::default_delete<int>>, std::allocator<std::unique_ptr<int, std::default_delete<int>>>>>>>::_M_default_append' requested here
_M_default_append(__new_size - size());
^
test.cpp:7:7: note: in instantiation of member function 'std::vector<std::queue<std::unique_ptr<int, std::default_delete<int>>, std::deque<std::unique_ptr<int, std::default_delete<int>>, std::allocator<std::unique_ptr<int, std::default_delete<int>>>>>, std::allocator<std::queue<std::unique_ptr<int, std::default_delete<int>>, std::deque<std::unique_ptr<int, std::default_delete<int>>, std::allocator<std::unique_ptr<int, std::default_delete<int>>>>>>>::resize' requested here
v.resize(10);
^
/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/include/g++-v10/bits/unique_ptr.h:468:7: note: 'unique_ptr' has been explicitly marked deleted here
unique_ptr(const unique_ptr&) = delete;
^
2 errors generated.
这似乎可以很好地与libc++配合使用，例如clang++ test.cpp -o test -stdlib=libc++。
这是一个已知的libstdc++错误吗？你知道如何解决这个问题吗？
这不是一个bug。std::queue<std::unique_ptr<int>>的Move构造函数在libc++中是noexcept(true)，但在libstdc++中不是。因此，对于libstdc++，std::vector必须使用复制构造函数进行重新分配。但它的调用会产生编译器错误，因为自然地，一个唯一指针队列可能不会被复制。
证明：https://godbolt.org/z/9j9P59
请注意，这不是一个bug，因为标准没有将std::queue的移动构造函数指定为noexcept。然而，允许实现来加强异常规范：
实现可以通过添加非抛出异常规范来加强非虚拟函数的异常规范。
这就是libc++在这里所做的：https://github.com/llvm/llvm-project/blob/master/libcxx/include/queue#L241.
如果您通读libstdc++的源代码，在vector的resize中，它最终调用
std::__uninitialized_move_if_noexcept_a
函数将旧内存空间移动或复制到新内存空间。
这个函数所做的是，如果move构造函数没有抛出，则移动底层对象，否则复制它
如果您通读了std:：queue对libstdc++的实现，则
template<typename _Alloc, typename _Requires = _Uses<_Alloc>>
queue(queue&& __q, const _Alloc& __a)
: c(std::move(__q.c), __a) { }
后面显然没有noexcept，这意味着它可能会投掷。因此，libstdc++将在调整大小时调用队列的复制构造函数，并且std:：unique_ptr无法复制，因此存在编译错误。
坦率地说，这应该在c++11之后工作，即使它不是一个bug，而是c++11之前的旧行为。