unique_ptr麻烦？ （VS 2015）

Question

我刚从这里复制了一些代码http://en.cppreference.com/w/cpp/language/pimpl，添加了<memory>和main.cpp，更正了std::experimental::propagate_const<std::unique_ptr<impl>>。 Visual Studio 2015。

// widget.h
#include <memory>

class widget
{
    // public members
private:
    struct impl;
    std::unique_ptr<impl> pImpl;
};

// widget.cpp
#include "widget.h"

struct widget::impl {
    // implementation details
};

widget.cpp编译得很好，但main.cpp不是。

#include "widget.h"

int main()
{
    widget w;
}

错误讯息。

1>c:\program files (x86)\microsoft visual studio 14.0\vc\include\memory(1193): error C2027: use of undefined type 'widget::impl'
1>  e:\***\***\***\widget.h(8): note: see declaration of 'widget::impl'
1>  c:\program files (x86)\microsoft visual studio 14.0\vc\include\memory(1192): note: while compiling class template member function 'void std::default_delete<_Ty>::operator ()(_Ty *) noexcept const'
1>          with
1>          [
1>              _Ty=widget::impl
1>          ]
1>  c:\program files (x86)\microsoft visual studio 14.0\vc\include\memory(1397): note: see reference to function template instantiation 'void std::default_delete<_Ty>::operator ()(_Ty *) noexcept const' being compiled
1>          with
1>          [
1>              _Ty=widget::impl
1>          ]
1>  c:\program files (x86)\microsoft visual studio 14.0\vc\include\memory(1227): note: see reference to class template instantiation 'std::default_delete<_Ty>' being compiled
1>          with
1>          [
1>              _Ty=widget::impl
1>          ]
1>  c:\program files (x86)\microsoft visual studio 14.0\vc\include\memory(1236): note: see reference to class template instantiation 'std::_Get_deleter_pointer_type<_Ty,std::default_delete<_Ty>>' being compiled
1>          with
1>          [
1>              _Ty=widget::impl
1>          ]
1>  c:\program files (x86)\microsoft visual studio 14.0\vc\include\memory(1279): note: see reference to class template instantiation 'std::_Unique_ptr_base<_Ty,_Dx>' being compiled
1>          with
1>          [
1>              _Ty=widget::impl,
1>              _Dx=std::default_delete<widget::impl>
1>          ]
1>  e:\***\***\***\***.h(10): note: see reference to class template instantiation 'std::unique_ptr<widget::impl,std::default_delete<_Ty>>' being compiled
1>          with
1>          [
1>              _Ty=widget::impl
1>          ]
1>c:\program files (x86)\microsoft visual studio 14.0\vc\include\memory(1194): error C2338: can't delete an incomplete type
1>c:\program files (x86)\microsoft visual studio 14.0\vc\include\memory(1195): warning C4150: deletion of pointer to incomplete type 'widget::impl'; no destructor called
1>  e:\***\***\***\widget.h(8): note: see declaration of 'widget::impl'

Answer 1

问题是std::unique_ptr有一个与之关联的删除者。如果未指定删除者，则默认为std::default_delete。

它做了什么？它在其上调用delete，这需要在该点定义析构函数。这需要在那里定义。

Answer 2

在单独的cpp中定义Widget的析构函数为空。在cpp中包含impl的定义。 impl的析构函数在cpp中调用，因为你包含了定义。