Issue importing functions from DLL C++. LNK 2001

Question

I have two projects. One creates a DLL and the other should use functions declared in the DLL, but I have problems implementing this.

In the DLL project I have these declarations:

using namespace XClass;

extern "C" __declspec(dllexport) int Compute(XClass::XClassInput input, XClassOutput &XClassOutput);

extern "C" __declspec(dllexport) int Init( string configFileName);

class xclass
{

public:
    xclass(void);
    xclass(constellation &Constellation, XClass::XClassConfig &XClassConfig);

    void   ComputeWeightingMatrix(constellation &xclass_constellation, char flagIntCont);
    void   ComputeGMatrix(constellation &Constellation, XClass::XClassInput &input);

private:
    int _numberOfSystemStates;
};

In the project that has to use the DLL functions I have this:

int _tmain(int argc, _TCHAR* argv[])
{

    XClass::XClassConfig xClassConfig;
    XClassOutput xClassOutput;

    XClass::XClassInput input;

    init(input, xClassOutput ); 

    constellation* class_constellation = new constellation(input, xClassConfig);

    xclass* algorithm = new xclass(*xclass_constellation, xClassConfig);


     algorithm->ComputeWeightingMatrix(*xclass_constellation,  'i');


    return 0;
}

The code for the ComputeWeighting Matrix function:

    void xclass::ComputeWeightingMatrix(constellation &Constellation, char flagIntCont)
    {
        double sigma = 0.0;
        long error;

            ...
    }

When I try to build I get his:

error LNK2001: unresolved external symbol "public: void __thiscall xclass::ComputeWeightingMatrix(class constellation &,char)" (?ComputeWeightingMatrix@xclass@@$$FQAEXAAVconstellation@@D@Z)

Answer 1

After some discussion in Chat, it turns out there are two parts to the solution of this problem:

1. Need to use the stub library from the DLL class.
2. Need to use class __declspec(dllexport) XClass to ensure the functionality from the class is exported.