Code worked in VS6 but not in VS2017

[Alan9]

The following code worked before with VS6 VC++. But it does not complete the compiling with VS2017 VC++ (Link error is shown below). The complete template is in a .h file. What was changed in VS2017? What needs to be done to resolve the error? Please help. Thanks.

error LNK2019: unresolved external symbol "class CArrayEx<double,double> __cdecl operator-(class CArrayEx<double,double> const &,class CArrayEx<double,double> const &)" (??G@YA?AV?$CArrayEx@NN@@ABV0@0@Z) referenced in function "public: int __thiscall CMathEx::QNSS(class CArrayEx<double,double> const &,class CArrayEx<double,double> &,class CArrayEx<double,double> &,double &,double &,int &,int)" (?QNSS@CMathEx@@QAEHABV?$CArrayEx@NN@@AAV2@1AAN2AAHH@Z)

//
template<class TYPE, class ARG_TYPE> 
class CArrayEx : public CArray<TYPE,ARG_TYPE>
{
public:
	CArrayEx(){}
	......
	friend CArrayEx<TYPE,ARG_TYPE>	operator + (const CArrayEx<TYPE,ARG_TYPE>& za1,const CArrayEx<TYPE,ARG_TYPE>& za2);
	......
};

template<class TYPE, class ARG_TYPE> 
CArrayEx<TYPE,ARG_TYPE> operator + (const CArrayEx<TYPE,ARG_TYPE>& za1,const CArrayEx<TYPE,ARG_TYPE>& za2)
{
	CArrayEx<TYPE,ARG_TYPE> za;
	za.SetSize(min(za1.GetSize(),za2.GetSize()));

	for (int i=0;i<za.GetSize();i++)
	{
		za[i]=za1[i]+za2[i];
	}
	return za;
}

[Marc G]

You are using operator-.
Do you have an implementation for that operator? I only see operator+ in the code snippet you showed.
Also, where are your implementations? In the header file itself? Somewhere else?

[2kaud]

[When posting code, please use code tags so that the code is readable. Go Advanced, select the formatted code and click '#'.]

There was massive changes in c++ between VS6 and VS2017. Also huge changes in the MS compiler used. As a consequence c++ code that compiled ok for VS6 may well not compile for VS2017. Many of us went through this pain a few years ago with VS2013/VS2015.

As Marc says in post #2, the problem is that operator- is being used in

CMathEx::QNSS(class CArrayEx<double,double> const &,class CArrayEx<double,double> &,class CArrayEx<double,double> &,double &,double &,int &,int)

but a definition can't be found.

[Marc G]

The massive changes between VC++ 6.0 and 2017 that 2kaud mentioned are a good thing
VC++ 6.0 was not really a good compiler, and was not standard compliant.
Recent compiler versions are much more, almost fully, standard compliant.

[Alan9]

You are using operator-.
Do you have an implementation for that operator? I only see operator+ in the code snippet you showed.
Also, where are your implementations? In the header file itself? Somewhere else?

Thanks for your reply.
I do have operators +/-/* in the definition (only friend CArrayEx<TYPE,ARG_TYPE> operator + is listed above as an example). The implementations are right below the class definition as shown above (operator + was provided above as an example, in the header file itself). But the VS2017 Linker does not seem to see this implementation. What is the workaround? Thanks for your help.

[Marc G]

Try the following syntax for your friend declaration:

friend CArrayEx<TYPE,ARG_TYPE> operator-<TYPE,ARG_TYPE>(const CArrayEx<TYPE,ARG_TYPE>& za1,const CArrayEx<TYPE,ARG_TYPE>& za2);

Such a friend declaration is tricky: you have to specify that for an instance of the template with types <TYPE, ARG_TYPE>, the <TYPE, ARG_TYPE> instantiation of operator- is a friend.

[Alan9]

Try the following syntax for your friend declaration:

friend CArrayEx<TYPE,ARG_TYPE> operator-<TYPE,ARG_TYPE>(const CArrayEx<TYPE,ARG_TYPE>& za1,const CArrayEx<TYPE,ARG_TYPE>& za2);

Such a friend declaration is tricky: you have to specify that for an instance of the template with types <TYPE, ARG_TYPE>, the <TYPE, ARG_TYPE> instantiation of operator- is a friend.

I tried it. But it does not compile. Do you have an example for implementing this type of operators? Thanks.

[Marc G]

Here is a very simple example that compiles just fine in VC++2017:

template<class TYPE, class ARG_TYPE>
class CArrayEx
{
public:
	CArrayEx() {}
	friend CArrayEx<TYPE, ARG_TYPE>	operator+<TYPE, ARG_TYPE>(const CArrayEx<TYPE, ARG_TYPE>& za1, const CArrayEx<TYPE, ARG_TYPE>& za2);
private:
	int m_i;
};

template<class TYPE, class ARG_TYPE>
CArrayEx<TYPE, ARG_TYPE> operator+(const CArrayEx<TYPE, ARG_TYPE>& za1, const CArrayEx<TYPE, ARG_TYPE>& za2)
{
	CArrayEx<TYPE, ARG_TYPE> za;
	za.m_i = za1.m_i + za2.m_i;
	cout << za.m_i << endl;
	return za;
}

int main()
{
	CArrayEx<int, double> e1, e2;
	e1 + e2;
	return 1;
}

If you still get errors, please post your code.