#ifndef MYFUNCTION_H
#define MYFUNCTION_H
#include <iostream>

class Myfunction
{
public:
    Myfunction();
    static void log(char info);
};

#endif // MYFUNCTION_H

#include "myfunction.h"

Myfunction::Myfunction()
{

}

void Myfunction::log(char info)
{
    std::cout << info;
}

g++ myfunction.cpp -I D:\work\CppSpace\Testdll  -shared -o myfunction.dll

#include <iostream>
#include "myfunction.h"
int main(int argc, char *argv[])
{
    std::cout << "main:" << std::endl;

    Myfunction::log(‘c‘);
    getchar();
    return 0;
}

g++ myfunction.dll main.cpp -o my.exe