#include <string>
#include <iostream>
#include <fstream>
#include <unistd.h>

int main()
{
  std::string name = std::string(getlogin());
  if (name.length()==0)
  {
      std::cout << "Error en getlogin()" << std::endl;
  }
  else
  {
      std::ofstream f("/home/" + name + "/Escritorio/log.txt");
      f << "Lo que quieras guardar " << std::endl;
      f.close();
  }
  return 0;
}