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QuestionC++ lambda callbacks, how to initialize with NULL pointer ? Pin
Member 853403512-Sep-15 0:45
MemberMember 853403512-Sep-15 0:45 
Hi all,

I need callback functions between different classes. I had already a solution based on stl, which was compilable with VS2010. Unfortunately I was not able to find a way to compile it with VS2015. I got weird error messages.

Now I found a solution with lamda C++11 lambda function pointers. Actually it works, but I have one open issue.

For having a save source code, I want to initialize the function pointer with NULL. But compiler is producing weird error messages again!

My Code:

typedef std::function<bool(int, int, CString*)> _tcedit_cb_;

class MyClass 
{
public:
   MyClass ()
   {
	m_cbGetItemData = NULL;  // <--- compile error because of the NULL pointer 
   }
   _tcedit_cb_ m_cbGetItemData;

   ...
}


How I can initialize the function callback pointer? I need to initialize in order to avoid running into illegal code!

e.g. I tried to cast ... = (_tcedit_cb_) NULL;

error messages:
c:\program files(x86)\microsoft visual studio 14.0\vc\include\type_traits(1501) : error C2893 : Failed to specialize function template 'unknown-type std::invoke(_Callable &&,_Types &&...)'
	1>  c:\program files(x86)\microsoft visual studio 14.0\vc\include\type_traits(1501) : note : With the following template arguments :
	1>  c:\program files(x86)\microsoft visual studio 14.0\vc\include\type_traits(1501) : note : '_Callable=_Decayed &'
	1>  c:\program files(x86)\microsoft visual studio 14.0\vc\include\type_traits(1501) : note : '_Types={int, int, ATL::CStringT<wchar_t,StrTraitMFC<wchar_t,ATL::ChTraitsCRT<wchar_t>>> }'
	1>  c:\program files(x86)\microsoft visual studio 14.0\vc\include\functional(210) : note : see reference to function template instantiation '_Rx std::_Invoke_ret<_Rx,_Callable&,_Ty,_Ty,ATL::CStringT<wchar_t,StrTraitMFC<wchar_t,ATL::ChTraitsCRT<wchar_t>>>>(std::_Forced<_Rx,false>,_Callable &,_Ty &&,_Ty &&,ATL::CStringT<wchar_t,StrTraitMFC<wchar_t,ATL::ChTraitsCRT<wchar_t>>> &&)' being compiled
	1>          with
	1>[
		1>              _Rx = bool,
			1>              _Callable = _Decayed,
			1>              _Ty = int
			1>]

AnswerRe: C++ lambda callbacks, how to initialize with NULL pointer ? Pin
Richard Andrew x6414-Sep-15 11:36
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GeneralRe: C++ lambda callbacks, how to initialize with NULL pointer ? Pin
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Questiondata structure and algoritm Pin
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