using namespace std;
#if __GNUC__ > 2
-ostream *open_file_stream (std::string file_name,
+ostream *open_file_stream (string file_name,
ios_base::openmode mode = ios::out);
#else
-ostream *open_file_stream (std::string file_name, int mode = ios::out);
+ostream *open_file_stream (string file_name, int mode = ios::out);
#endif
void close_file_stream (ostream *os);