extern std::string& to_lower(std::string& str);
extern bool is_number(const std::string& str);
std::vector <std::string> split(std::string str, char d);
-/* Comment out to_string functions when they are defined already - C++ 11 defines these */
+
+// libc++ has these as built-ins for all C++ language versions
+#if !defined(_LIBCPP_VERSION)
extern std::string to_string(int);
extern std::string to_string(double);
extern std::string to_string(float);
+#endif
+
extern std::string replace(std::string str, const std::string& old, const std::string& newstr);
#else
#include <cctype>