FIFO problemss.. Please help? =)

[c3jcarmy]

Hi There,

I have an embarrassing problem with fifo.. I have to write two programs, named write and read. The write program has to copy a plain text file to stdout and the read program has to read the stdin then count number of bytes in the stream. It is a process synchronization problem, the way I approach it is by fifo.. Then I made these programs as following..

write.c

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

char *fifo = "fifo";

int main() {
	FILE *fp;
	char *buffer;
	int fd, nwrite;
	unsigned long length;

	if((fp = fopen("test.txt", "r")) < 0) {
		printf("write-main: cannot open test.txt\n");
	}
	fseek(fp, 0, SEEK_END);
	length = ftell(fp);
	fseek(fp, 0, SEEK_SET);

		// Allocate memory
	buffer = (char *)malloc(length+1);
	if(!buffer) {
		printf("write-main: memory error\n");
		fclose(fp);
		return;
	}
	
	// Read file content into buffer
	fread(buffer, length, 1, fp);
	fclose(fp);

	if(mkfifo(fifo, 0666) == -1) {
		printf("write-main: cannot create fifo\n");
	} else {
		if((fd = open(fifo, O_WRONLY | O_NONBLOCK)) < 0) {
			printf("write-main: fifo open failed\n");
		} else {
			if((nwrite = write(fd, buffer, length)) == -1) {
				printf("write-main: message write failed\n");
			}
		}
	}
}

read.c

#include <stdlib.h>
#include <stdio.h>
#include <fcntl.h>
#define MSGSIZE	100

char *fifo = "fifo";

int main() {
	FILE *fp;
	unsigned long length;
	char *buffer;
	int fd;

	if((fd = open(fifo, O_RDWR)) < 0) {
		printf("read-main: cannot open fifo\n");
	} else {
		if((read(fd, buffer, length)) < 0) {
			printf("read-main: message read failed\n");
		}
	}
	printf("message recieve:%s\n", buffer);
}

These two programs compile perfectly, but when i try to run it.. It shows the "write-main: fifo open failed" which means it couldn't open the fifo that created at runtime.. I made these two programs since I thought that fifo is the best way to tackle this problem, is there any other suggestion how to solve this? Thank you...

[cas]

If you open a FIFO in non-blocking mode, something has to be attached to the other end. Because there isn't anything, the open fails.

In addition, you should not use O_RDWR with a FIFO; it's undefined according to POSIX.

There are a number of other issues that you will find if you build with -Wall (assuming you're using gcc).