c++ - String function does not return -

i've written piece of code. there's class rational numerator , denominator private members. there method tostring() should return rational number string ("numerator/denominator"). unknown reasons me, not return anything. code:

#include <iostream> #include <iomanip> #include <string> #include <sstream>  using namespace std;  class rational {     long int n, d; public:     rational(long int n, long int d) {         this->n = n;         this->d = d;     }     bool equals();     int compareto();     std::string tostring() {         string resn, resd;         string str;         ostringstream convertn, convertd;         convertn << this->n;         convertd << this->d;         resn = convertn.str();         resd = convertd.str();          str = resn + "/" + resd;         return str;     } };  int main() {     rational rat(2, 3);     rat.tostring();      return 0; } 

first thought conversion algorithm wrong, , tried returning anything, still nothing. thank in advance.

if want output string, use cout << rat.tostring();