#include <sys/types.h>
#include <sys/stat.h>
#include <stdlib.h>
#include <stdio.h>
#include <math.h>
#include <unistd.h>

#define PANIC(a) do { \
                perror(a); \
                if (temp_name) unlink(temp_name);\
                exit(1);\
        } while(0)

int main() {
    FILE *command,*data;
    char *temp_name;
    double a,b;
    int i;

    if ((temp_name = tmpnam((char *) 0)) == 0) PANIC("tmpnam failed");
    if(mkfifo(temp_name, S_IRUSR | S_IWUSR) != 0) PANIC("mkfifo failed");
    command = popen("gnuplot","w");
    fprintf(command,"plot \"%s\" with lines\n",temp_name); fflush(command);
    data = fopen(temp_name,"w");
    for (i=0; i<20; i++) {
        a = i/10.0;
        b = sin(a);
        fprintf(data,"%f %f\n",a,b);
    }
    fclose(data);
    fprintf(stderr,"press enter to continue..."); fflush(stderr);
    getchar();

    fprintf(command,"plot \"%s\" with lines\n",temp_name); fflush(command);
    data = fopen(temp_name,"w");
    for (i=0; i<20; i++) {
        a = i/10.0;
        b = cos(a);
        fprintf(data,"%f %f\n",a,b);
    }
    fclose(data);
    fprintf(stderr,"press enter to continue..."); fflush(stderr);
    getchar();
    fclose(command);
    unlink(temp_name);
    return 0;
}