More *nix pipe blues.. I can't get gnuplot to display the plot.

I can't get gnuplot to display the plot of sin(5). Here is what I've attempted...

Code:

---

#include <stdio.h>
#include <stdlib.h>

int main(void)
{
  FILE *command;

  if ((command = popen("gnuplot", "w")) == NULL) {
    (void)fprintf(stderr, "pipe error\n");
    exit(1);
  }

  if (setvbuf(command, NULL, _IONBF, 0) != 0) {
    (void)fprintf(stderr, "setbuf error\n");
    exit(1);
  }

  (void)fprintf(command, "plot \"%s\" ", "sin(5)");
  /*fflush(command);*/

  pclose(command);
  exit(0);
}

---

But when I compile and run it, the program just exits. Below is what I get

Quote:

---

$ gcc -Wall -Wextra dd2.c -o dd2
$ ./dd2
$ echo $?
0
$

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Never mind. I figured it out. For whatever reasons, I needed a newline in the following line code..

Code:

---

(void)fprintf(command, "plot \"%s\" ", "sin(5)");

---

So I changed the code to the following.

Code:

---

(void)fprintf(command, "%s\n", "plot sin(5)");

---

Also, I needed to have the follow so the plotter wouldn't exit right away..

Code:

---

while ((c = getchar()) != EOF)
    ;

---

Anyways, here is the complete solution..

Code:

---

#include <stdio.h>
#include <stdlib.h>

int main(void)
{
  FILE *command;
  int c;

  if ((command = popen("gnuplot", "w")) == NULL) {
    (void)fprintf(stderr, "pipe error\n");
    exit(1);
  }

  if (setvbuf(command, NULL, _IONBF, 0) != 0) {
    (void)fprintf(stderr, "setbuf error\n");
    exit(1);
  }

  (void)fprintf(command, "%s\n", "plot sin(5)");
  fflush(command);

  while ((c = getchar()) != EOF)
    ;

  pclose(command);
  exit(0);
}

---

Now, I have one more question. Why does gnuplot exit right away when I don't include

Code:

---

while ((c = getchar()) != EOF)
    ;

---

but something like ddd (the data display debugger) doesn't?