std :: vector不会使用noexcept移动构造的对象调用移动构造函数

Question

我最近一直在使用移动和复制构造器进行了大量的工作,而且似乎无法找到我自己的awnser.结构相当简单.一个类OWUP,它将一个std :: unique_ptr保存到一个对象(在这个例子中是一个int),一个类是一个简单的包装器,它是一个简单的包装器,它是围绕着OWUP的std :: vector和类二,它是一个简单的包装器std :: vector of One的.

#include <memory>
#include <vector>

class OWUP {
public:
    OWUP()
    : data(nullptr)
    { }

    OWUP(const OWUP &) = delete;
    OWUP &operator=(const OWUP &) = delete; 
    OWUP(OWUP &&) noexcept = default;
    OWUP &operator=(OWUP &&) noexcept = default; 

    std::unique_ptr<int> data; 
};

class One {
public:
    One(std::size_t numof_datas)
    : datas(numof_datas)
    { }

    One(const One &) = delete;
    One &operator=(const One &) = delete; 
    One(One &&) noexcept = default;
    One &operator=(One &&) noexcept = default; 

    std::vector<OWUP> datas;
};

class Two {
public:
    Two(std::size_t numof_ones, std::size_t num_of_datas)
    : ones(numof_ones, One(num_of_datas))
    { }

    Two(const Two &) = delete;
    Two &operator=(const Two &) = delete; 
    Two(Two &&) noexcept = default;
    Two &operator=(Two &&) noexcept = default;

    std::vector<One> ones;
}; 

代码获取以下错误代码 g++ -std=c++14 example.cpp

In file included from /usr/include/c++/7.3.1/memory:64:0,
                 from example.cpp:1:
/usr/include/c++/7.3.1/bits/stl_construct.h: In instantiation of 'void std::_Construct(_T1*, _Args&& ...) [with _T1 = One; _Args = {const One&}]':
/usr/include/c++/7.3.1/bits/stl_uninitialized.h:210:18:   required from 'static _ForwardIterator std::__uninitialized_fill_n<_TrivialValueType>::__uninit_fill_n(_ForwardIterator, _Size, const _Tp&) [with _ForwardIterator = One*; _Size = long unsigned int; _Tp = One; bool _TrivialValueType = false]'
/usr/include/c++/7.3.1/bits/stl_uninitialized.h:255:17:   required from '_ForwardIterator std::uninitialized_fill_n(_ForwardIterator, _Size, const _Tp&) [with _ForwardIterator = One*; _Size = long unsigned int; _Tp = One]'
/usr/include/c++/7.3.1/bits/stl_uninitialized.h:366:39:   required from '_ForwardIterator std::__uninitialized_fill_n_a(_ForwardIterator, _Size, const _Tp&, std::allocator<_Tp2>&) [with _ForwardIterator = One*; _Size = long unsigned int; _Tp = One; _Tp2 = One]'
/usr/include/c++/7.3.1/bits/stl_vector.h:1337:33:   required from 'void std::vector<_Tp, _Alloc>::_M_fill_initialize(std::vector<_Tp, _Alloc>::size_type, const value_type&) [with _Tp = One; _Alloc = std::allocator<One>; std::vector<_Tp, _Alloc>::size_type = long unsigned int; std::vector<_Tp, _Alloc>::value_type = One]'
/usr/include/c++/7.3.1/bits/stl_vector.h:298:27:   required from 'std::vector<_Tp, _Alloc>::vector(std::vector<_Tp, _Alloc>::size_type, const value_type&, const allocator_type&) [with _Tp = One; _Alloc = std::allocator<One>; std::vector<_Tp, _Alloc>::size_type = long unsigned int; std::vector<_Tp, _Alloc>::value_type = One; std::vector<_Tp, _Alloc>::allocator_type = std::allocator<One>]'
example.cpp:40:39:   required from here
/usr/include/c++/7.3.1/bits/stl_construct.h:75:7: error: use of deleted function 'One::One(const One&)'
     { ::new(static_cast<void*>(__p)) _T1(std::forward<_Args>(__args)...); }
       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
example.cpp:29:3: note: declared here
   One(const One &) = delete;
   ^~~

我已经尽力强迫它使用移动构造函数.我还尝试使用std :: move创建自己的移动构造函数,但这导致了相同的编译错误.我知道std :: vector测试了move_if_noexcept(),但是为了找不到它为什么没有.我做错了什么？

Answer 1

因为问题在这里:

Two(std::size_t numof_ones, std::size_t num_of_datas)
: ones(numof_ones, One(num_of_datas))
{ }

你不能离开One你在这里创建,你真的需要从它复制numof_ones时间.