string to_string (long unsigned);
string to_string (unsigned);
string to_string (bool b);
-string to_string (char const *format, ...);
+string to_string (char const *format, ...)
+ __attribute__ ((format (printf, 1, 2)));
string &replace_all (string &str, string find, string replace);
string &replace_all (string &str, char find, char replace);