+string to_string (string s);
+string to_string (char c, int n = 1);
+string to_string (int i, char const *format = 0);
+string to_string (double f, char const *format = 0);
+string to_string (long);
+string to_string (long unsigned);
+string to_string (I64, char const *format = 0);
+string to_string (unsigned);
+string to_string (bool b);
+string to_string (char const *format, ...)
+__attribute__ ((format (printf, 1, 2)));