Question

I have this code:

CCalcArchive::CCalcArchive() : m_calcMap() { } 

m_calcMap is defined as this:

typedef CTypedPtrMap<CMapStringToPtr, CString, CCalculation*> CCalcMap; CCalcMap& m_calcMap; 

When I compile in Visual Studio 2008, I get this error:

error C2440: 'initializing' : cannot convert from 'int' to 'CCalcArchive::CCalcMap &' 

I don’t even understand where it gets the ‘int’ error from, and also why this doesn’t work? It feels like I’m actually having some sort of syntax error, but isn’t this how member initialization lists are supposed to be used? Also, AFAIK, the MFC class CTypedPtrMap has no constructor taking arguments.

Answer 1

The int is coming from the fact that CTypedPtrMap has a constructor that takes an int argument that is defaulted to 10.

The real problem that you’re running into is that the m_calcMap reference initalization you have there is trying to default construct a temporary CTypedPtrMap object to bind the reference to. However, only const references can be bound to temporary objects. No doubt the error message is not very informative.

But even if the m_calcMap member were a const refernce, you’d still have a problem binding it to a temporary. in this case, the MSVC 2008 compiler gives a pretty clear warning:

mfctest.cpp(72) : warning C4413: '' : reference member is initialized to a temporary                                         that doesn't persist after the constructor exits