Cで出力したファイルをリアルタイムでGnuplotに飛ばす

    
        #define _USE_MATH_DEFINES
        #include <math.h>
        #include <fstream>
        #include <iostream>
        using namespace std;
        void test(int tmp);
        int t;
        int t_max;
        double dt;
        int main(){
         int judge = 2;
         do{
          test(judge);
          FILE *hoge;
          hoge = _popen("gnuplot -persist", "w");
          fprintf_s(hoge, \
                    "plot 'test.dat' with lines lw 2 notitle \n");
          fflush(hoge);
          fprintf_s(hoge, "exit");
          _pclose(hoge);
          cout << "Do you finish ? 1:yes, 2:change, 3:continue" << endl;
          scanf("%d", &judge);
          if (judge == 1) break;
         } while (1);
         return 0;
        }
        
        void test(int tmp){
         if (tmp == 2){
          cout << "パラメータを指定してください" << endl;
          cout << "t_max=";
          scanf_s("%d", &t_max);
          cout << "dt=";
          scanf_s("%lf", &dt);
         }
         char filepath[100];
         sprintf(filepath, "test.dat");
         ofstream output(filepath, ios_base::trunc);
         for (t = 0; t < (int)(t_max / dt); t++){
          output << t << " " << sin(t) << endl;
         }
        }