or using the stringstreams:
#include <sstream>
#include <iomanip>
std::stringstream ss;
ss << std::setw(10) << std::setfill('0') << i;
std::string s = ss.str();
I compiled the information I found on arachnoid.com because I like the type-safe way of iostreams more. Besides, you can equally use this code on any other output stream.