#include <unistd.h> //gnuplot
#include<stdio.h>
#include<stdlib.h>
#include<math.h>
#include <string.h>
#define GNUPLOT "/usr/local/Cellar/gnuplot/5.4.0_1/bin/gnuplot" //gnuplotのパスを指定
int main(){
  FILE *gp ; //gnuplotのパイプ
  if((gp=popen(GNUPLOT " -persist", "w"))==NULL){
   printf("パイプがひらけません\n"); 
   exit(1) ;}

//cosの計算をsample.datに代入
FILE *fp;
char filename[30]="sample.dat";
fp=fopen(filename,"w");
for(double i=0;i<5;i=i+0.3){
fprintf(fp,"%f %f\n",i,cos(i));
}
fclose(fp);
//gnuplotで描写
fprintf(gp,"set title 'Trigonometric function(sin x)'\n");
fprintf(gp,"plot sin(x) notitle, 'sample.dat' with linespoints notitle\n");

fprintf(gp,"set terminal postscript eps enhanced solid color\n");
fprintf(gp,"set output 'gazou.eps'\n");
fprintf(gp,"replot\n");
fprintf(gp,"unset output\n");
pclose(gp);
return 0;
}