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社区首页 >问答首页 >如何调整std::vector<std::queue<std::unique_ptr<int>>>？的大小

问如何调整std::vector<std::queue<std::unique_ptr<int>>>？的大小
EN

Stack Overflow用户
提问于 2020-12-04 09:00:02
回答 2查看 350关注 0票数 4

我想做以下几件事：

代码语言：javascript
复制
#include <memory>
#include <vector>
#include <queue>

int main() {
    std::vector<std::queue<std::unique_ptr<int>>> v;
    v.resize(10);
}

但是我和GCC一起得到了10.2：

代码语言：javascript
复制
$ 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,
    |                                                                        ^~~~~

同样适用于clang++11

代码语言：javascript
复制
$ 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.

这在libc++中似乎很好，例如clang++ test.cpp -o test -stdlib=libc++。

我这是一个已知的libstdc++错误吗？知道怎么解决这个问题吗？

c++
gcc
libstdc++
compiler-bug
EN

回答 2

Stack Overflow用户

回答已采纳

发布于 2020-12-04 09:31:49

这不是窃听器。std::queue<std::unique_ptr<int>>的移动构造函数是noexcept(true)在libc++中，而不是在libstdc++中。因此，对于libstdc++，std::vector必须使用复制构造函数进行重新分配。但是它的调用会生成一个编译器错误，因为自然地，一个唯一指针的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，因为标准没有为std::queue规定移动构造函数为noexcept。然而，实现是允许加强异常规范

实现可以通过添加非抛出异常规范来增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。

票数 5
EN

Stack Overflow用户

发布于 2020-12-04 10:06:50

如果你阅读libstdc++的源代码，在向量的调整大小，它最终调用，

代码语言：javascript
复制
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。

此函数所做的是，如果移动构造函数不抛出，则移动底层对象，否则复制它。

如果您阅读std：：queue的libstdc++实现，

代码语言：javascript
复制
template<typename _Alloc, typename _Requires = _Uses<_Alloc>>
queue(queue&& __q, const _Alloc& __a)
   : c(std::move(__q.c), __a) { }

显然后面没有noexcept，这意味着它可能会抛出。因此，libstdc++将在调整大小时调用队列的复制构造函数，并且无法复制std::unique_ptr，因此存在编译错误。

坦率地说，这应该在c++11之后起作用，即使它不是一个bug，而是在前C++11时代的一种旧行为。

票数 0
EN
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：

https://stackoverflow.com/questions/65140603

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