Invalid application of 'sizeof' to incomplete type ( created classes)
c++
Solution
I modified to shared_ptr, but including the headers are still a option.
Here is the link for someone who may have same error here
Problem
I have next classes: State.hpp ``` ... class Engine; namespace window { class State { ... } } ``` WConsole.hpp ``` ... class Engine; namespace window { class Console: public State { .. } } ``` WMesssage.hpp ``` ... class Engine; namespace window { class Message: public State { ... } } ``` And all classes link to Engine class: Engine.hpp ``` ... namespace window { class State; class Console; class Message; } class Engine { ... std::vector< std::unique_ptr<window::State> > m_windowObjects; std::unique_ptr<window::Console> m_consoleWindow; std::unique_ptr<window::Message> m_messageWindow; ... } ``` And in Engine.cpp I include the headers: ``` #include "Engine.hpp" #include "WState.hpp" #include "WConsole.hpp" #include "WMessage.hpp" ``` If I try to compile I get this errors: ``` In file included from /usr/include/c++/4.8.2/memory:81:0, from /usr/local/include/SFGUI/Signal.hpp:6, from /usr/local/include/SFGUI/Object.hpp:4, from /usr/local/include/SFGUI/Widget.hpp:4, from /usr/local/include/SFGUI/Container.hpp:4, from /usr/local/include/SFGUI/Bin.hpp:4, from /usr/local/include/SFGUI/SFGUI.hpp:6, from ./include/Handler.hpp:4, from main.cpp:1: /usr/include/c++/4.8.2/bits/unique_ptr.h: In instantiation of 'void std::default_delete<_Tp>::operator()(_Tp*) const [with _Tp = window::Console]': /usr/include/c++/4.8.2/bits/unique_ptr.h:184:16: required from 'std::unique_ptr<_Tp, _Dp>::~unique_ptr() [with _Tp = window::Console; _Dp = std::default_delete<window::Console>]' ./include/Engine.hpp:21:7: required from here /usr/include/c++/4.8.2/bits/unique_ptr.h:65:22: error: invalid application of 'sizeof' to incomplete type 'window::Console' static_assert(sizeof(_Tp)>0, ^ /usr/include/c++/4.8.2/bits/unique_ptr.h: In instantiation of 'void std::default_delete<_Tp>::operator()(_Tp*) const [with _Tp = window::Message]': /usr/include/c++/4.8.2/bits/unique_ptr.h:184:16: required from 'std::unique_ptr<_Tp, _Dp>::~unique_ptr() [with _Tp = window::Message; _Dp = std::default_delete<window::Message>]' ./include/Engine.hpp:21:7: required from here /usr/include/c++/4.8.2/bits/unique_ptr.h:65:22: error: invalid application of 'sizeof' to incomplete type 'window::Message' ``` From what I see I don't get an error relating to window::State so mean that I introduced it in the right way, but why I get error relating to window::Console and window::Message? May affect that classes window::Console and window::Message are derivated from window::State?