DLL

//StuffDLL.h

#ifdef STUFFDLL_EXPORTS
#define STUFFDLL_API __declspec(dllexport)
#else
#define STUFFDLL_API __declspec(dllimport)
#endif

namespace Stuff {
    class StuffMath {
    public:
        template<class T> static STUFFDLL_API T Ad(T a, T b);
        static STUFFDLL_API double Add(double a, double b);
    };
}

// StuffDLL.cpp : Defines the exported functions for the DLL application.
//Turn off "precompiled headers"

#include "StuffDLL.h"
#include <stdexcept>

using namespace std;

namespace Stuff {
    double StuffMath::Add(double a, double b) {
        return (a + b);
    }

    template<class T>
    T StuffMath::Ad(T a, T b) {
        return(a + b);
    }
}

// DLLExec.cpp : Defines the entry point for the console application.

#include <iostream>
#include <Windows.h>
#include "StuffDLL.h"

using namespace std;

int main() {
    cout << "a + b = " << Stuff::StuffMath::Ad(2, 3) << endl;

    system("pause");
    return(0);
}