我試圖編譯一些代碼,這減少了這一點:爲什麼QString和vector <unique_ptr <int>>在這裏顯示爲不兼容?
#include <memory>
#include <vector>
#include <QString>
class Category
{
std::vector<std::unique_ptr<int>> data;
QString name;
};
int main()
{
std::vector<Category> categories;
categories.emplace_back();
};
編譯爲是,則在下面的錯誤是由於g ++以及用於鐺類似++:
In file included from /opt/gcc-4.8/include/c++/4.8.2/memory:64:0,
from test.cpp:1:
/opt/gcc-4.8/include/c++/4.8.2/bits/stl_construct.h: In instantiation of ‘void std::_Construct(_T1*, _Args&& ...) [with _T1 = std::unique_ptr<int>; _Args = {const std::unique_ptr<int, std::default_delete<int> >&}]’:
/opt/gcc-4.8/include/c++/4.8.2/bits/stl_uninitialized.h:75:53: required from ‘static _ForwardIterator std::__uninitialized_copy<_TrivialValueTypes>::__uninit_copy(_InputIterator, _InputIterator, _ForwardIterator) [with _InputIterator = __gnu_cxx::__normal_iterator<const std::unique_ptr<int>*, std::vector<std::unique_ptr<int> > >; _ForwardIterator = std::unique_ptr<int>*; bool _TrivialValueTypes = false]’
/opt/gcc-4.8/include/c++/4.8.2/bits/stl_uninitialized.h:117:41: required from ‘_ForwardIterator std::uninitialized_copy(_InputIterator, _InputIterator, _ForwardIterator) [with _InputIterator = __gnu_cxx::__normal_iterator<const std::unique_ptr<int>*, std::vector<std::unique_ptr<int> > >; _ForwardIterator = std::unique_ptr<int>*]’
/opt/gcc-4.8/include/c++/4.8.2/bits/stl_uninitialized.h:258:63: required from ‘_ForwardIterator std::__uninitialized_copy_a(_InputIterator, _InputIterator, _ForwardIterator, std::allocator<_Tp>&) [with _InputIterator = __gnu_cxx::__normal_iterator<const std::unique_ptr<int>*, std::vector<std::unique_ptr<int> > >; _ForwardIterator = std::unique_ptr<int>*; _Tp = std::unique_ptr<int>]’
/opt/gcc-4.8/include/c++/4.8.2/bits/stl_vector.h:316:32: required from ‘std::vector<_Tp, _Alloc>::vector(const std::vector<_Tp, _Alloc>&) [with _Tp = std::unique_ptr<int>; _Alloc = std::allocator<std::unique_ptr<int> >]’
test.cpp:5:7: [ skipping 2 instantiation contexts, use -ftemplate-backtrace-limit=0 to disable ]
/opt/gcc-4.8/include/c++/4.8.2/bits/stl_uninitialized.h:117:41: required from ‘_ForwardIterator std::uninitialized_copy(_InputIterator, _InputIterator, _ForwardIterator) [with _InputIterator = Category*; _ForwardIterator = Category*]’
/opt/gcc-4.8/include/c++/4.8.2/bits/stl_uninitialized.h:258:63: required from ‘_ForwardIterator std::__uninitialized_copy_a(_InputIterator, _InputIterator, _ForwardIterator, std::allocator<_Tp>&) [with _InputIterator = Category*; _ForwardIterator = Category*; _Tp = Category]’
/opt/gcc-4.8/include/c++/4.8.2/bits/stl_uninitialized.h:281:69: required from ‘_ForwardIterator std::__uninitialized_move_if_noexcept_a(_InputIterator, _InputIterator, _ForwardIterator, _Allocator&) [with _InputIterator = Category*; _ForwardIterator = Category*; _Allocator = std::allocator<Category>]’
/opt/gcc-4.8/include/c++/4.8.2/bits/vector.tcc:415:43: required from ‘void std::vector<_Tp, _Alloc>::_M_emplace_back_aux(_Args&& ...) [with _Args = {}; _Tp = Category; _Alloc = std::allocator<Category>]’
/opt/gcc-4.8/include/c++/4.8.2/bits/vector.tcc:101:54: required from ‘void std::vector<_Tp, _Alloc>::emplace_back(_Args&& ...) [with _Args = {}; _Tp = Category; _Alloc = std::allocator<Category>]’
test.cpp:14:29: required from here
/opt/gcc-4.8/include/c++/4.8.2/bits/stl_construct.h:75:7: error: use of deleted function ‘std::unique_ptr<_Tp, _Dp>::unique_ptr(const std::unique_ptr<_Tp, _Dp>&) [with _Tp = int; _Dp = std::default_delete<int>]’
{ ::new(static_cast<void*>(__p)) _T1(std::forward<_Args>(__args)...); }
^
In file included from /opt/gcc-4.8/include/c++/4.8.2/memory:81:0,
from test.cpp:1:
/opt/gcc-4.8/include/c++/4.8.2/bits/unique_ptr.h:273:7: error: declared here
unique_ptr(const unique_ptr&) = delete;
^
- 如果我從
Category
刪除name
成員,它編譯好。 - 如果我使
data
只是一個unique_ptr<int>
而不是一個指針向量,它編譯得很好。 - 如果我在
main()
中創建了一個單獨的Category
,而不是創建一個矢量並且執行emplace_back()
,它編譯得很好。 - 如果我用
std::string
代替QString
,它編譯得很好。
發生了什麼事?是什麼讓這個代碼不合格?是g ++ & clang ++的bug的結果嗎?
可能是因爲'QString'定義了一個拷貝構造函數,並且沒有移動構造函數,這意味着它的移動構造函數被隱式定義爲刪除。然後'emplace_back'調用將嘗試複製'unique_ptr',導致上面的錯誤。 – Praetorian
根據[this](http://doc.qt.io/qt-5/qstring.html#QString-6),'QString'的移動構造函數是在Qt5.2中引入的,你使用的是舊版本? – Praetorian
@Praetorian我在這裏使用Qt4。 – Ruslan