C++ long int與string互轉

#include <sstream>
#include <string>
long int stringtolong(std::string str)
{
    long int result;
    stringstream ss;
    ss <<  str;
    ss >> result;
    return result;
}
 
string longtostring(long int t)
{
    std::string result;
    stringstream ss;
    ss <<  t;
    ss >> result;
    return result;
}