Example
.......

::

    struct string_appender
    {
	string_appender(std::string& s)
	    : m_str(&s)
	{}

	void operator()(const std::string& x) const
	{
	    *m_str += x;
	}

	std::string* m_str;
    };

    int main(int, char*[])
    {
      std::vector<std::string> x;
      x.push_back("hello");
      x.push_back(" ");
      x.push_back("world");
      x.push_back("!");

      std::string s = "";
      std::copy(x.begin(), x.end(), 
		boost::make_function_output_iterator(string_appender(s)));

      std::cout << s << std::endl;

      return 0;
    }