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

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?