How do I convert a long to a string in C++?

In C++11, there are actually std::to_string and std::to_wstring functions in <string>.

string to_string(int val);
string to_string(long val);
string to_string(long long val);
string to_string(unsigned val);
string to_string(unsigned long val);
string to_string(unsigned long long val);
string to_string(float val);
string to_string(double val);
string to_string (long double val);