How to loop a FIFO reader program in C - c

Question

I'm writing a c program in ubuntu that writes and reads in fifo pipe. I already have the program writing working perfectly, I now have a problem reading in a loop.
My reading program :
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <fcntl.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#define MAX_CTRLS 80
void main()
{
printf("test1");
char ch2[MAX_CTRLS];
int pipe1;
pipe1 = open("/tmp/ctrl", O_RDONLY);
printf("test2");
read(pipe1, ch2, MAX_CTRLS);
printf("%s",ch2);
close(pipe1);
}
This program is supposed to read in the fifo, store it in ch2 then print in ch2. But when running it normally it works perfectly, while running it in a loop, it doesn't do anything.
Here is writing program 1 :
void send(char ch2[MAX_CTRLS])
{
int create;
create = mkfifo("/tmp/ctrl", 0666);
int pipe1;
pipe1 = open("/tmp/ctrl", O_WRONLY);
write(pipe1, ch2, MAX_CTRLS);
close(pipe1);
}
This one works using another program I have, that has a line like this :
ch2[0] = 'a';
printf("%s",ch2);
send(ch2);
The printf helps me confirm that ch2 is set properly. I need the reading program to loop the reading function, aka print everytime what is set in ch2.
I just ant it to print a in this case, everytime my program launches send(ch2).
Thaks in advance

Answer 1

I figure you want to have a loop that open the pipe and reads if anything is there, with no delay, then goes to sleep for a while before next reading.
Suggest something like this, u might also swap for(;;) to While(boolValue == true)
int fd = -1, naptime = 200; // 200msec
for (;;){
fd = open(pipe, mode|nodelay);
if (fd != -1){
int st = read (fd, buf, sizeof(buf)); /* open OK */
// do your printing of data if any exist - st holds read chars
if(st >0) printf(buf);
}
sleep(naptime); // sleep til next reading
}

Answer 2

I need the reading program to loop the reading function, aka print everytime what is set in ch2.
Simply adding a while(1) to run the reading program on a loop won't do good, because read() from a FIFO that has been closed (which is the case after the first run of the writing program) doesn't block, but rather returns 0, and we surely don't want a busy waiting read() loop. So, we need a means of waiting for something readable from the FIFO. If we have the fortune to run Linux, we can use inotify to get notified of writings to the FIFO. The reading code could be:
#include <sys/inotify.h>
int fd = inotify_init();
inotify_add_watch(fd, "/tmp/ctrl", IN_MODIFY);
pipe1 = open("/tmp/ctrl", O_RDONLY);
struct inotify_event inev;
while (read(fd, &inev, sizeof inev))
if (read(pipe1, ch2, MAX_CTRLS) > 0)
printf("%s", ch2), fflush(stdout);