fopen hangs. I'm trying to simulate 'cat test.txt | wall"

The following programs 'hangs' at this point.

Code:

if ((data = fopen(temp_name,"w")) == NULL) {
    (void)fprintf(stderr, "cant open temp_name file\n");
    exit(1);
  }

Given the following

Code:

#include <stdio.h>
#include <stdlib.h>
#include <sys/time.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/wait.h>
#include <unistd.h>
#include <fcntl.h>

#include <signal.h>


int main(void) {
  FILE *command;
  FILE *data;
  char *temp_name;
  int i = 0;

  if ((temp_name = tmpnam(NULL)) == 0) {
    (void)fprintf(stderr, "cant create temp file\n");
    exit(1);
   }

  printf ("Tempname #2: %s\n",temp_name);

  if(mkfifo(temp_name, S_IRUSR | S_IWUSR) != 0) {
    (void)fprintf(stderr, "cant create fifo\n");
    exit(1);
  }

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

  (void)fprintf(command, "cat \"%s\" ", temp_name);
  fflush(command);

 /*fopen doesn't return*/
  if ((data = fopen(temp_name,"w")) == NULL) {
    (void)fprintf(stderr, "cant open temp_name file\n");
    exit(1);
  }


  for(i = 0; i < 10; i++) {
    (void)fprintf(data,"%s\n", "test");
  }

  fclose(data);
  fclose(command);
  unlink(temp_name);
  
  exit(0);
}

And here is what I get when I try to run it..

$ gcc -g -Wall -Wextra broad3.c -o broad3
/tmp/cczlHIZZ.o: In function `main':
/home/cdalten/oakland/broad3.c:19: warning: the use of `tmpnam' is dangerous, better use `mkstemp'
[cdalten@localhost oakland]$ ./broad3
Tempname #2: /tmp/filejEugU4

Why is fopen() not returning?

Well so far, all you've managed is
echo "cat tempname" | wall

You then write a bunch of stuff to your temp file, then delete it.

An attempt to open one end of a FIFO will hang until somebody else opens the other end. Read the manual.