Thread: Directories as regular files

Hello guys, I wasn't sure whether I should post this here or in a Linux forum. Forgive me if I'm wrong. The problem is the following: aren't Linux directories just regular files that have a list of other files as their contents? So why this dummy code works with a regular file but prints "error reading dir" with a directory?

Code:

	char *file = "dir";
	int fd;
	
	if ((fd = open(file, O_RDONLY)) == -1)
		printf("error opening %s\n", file);
	
	char buffer[1024];
	
	int n;
	if((n = read(fd, &buffer, 1024)) == -1)
		printf("error reading %s\n", file);
	
	int i;
	for (i = 0; i < n; ++i)
		printf("%c", buffer[i]);

Perhaps directories are different from regular files in Linux? That would be strange. In Unix they are the same or so they are treated in the simple implementation of opendir, readdir, etc in K&R2. Any hints?

Thanks in advance for your help

Check errno after trying to read. You're probably getting EISDIR. According to POSIX, EISDIR is set when “[t]he fildes argument refers to a directory and the implementation does not allow the directory to be read using read() or pread(). The readdir() function should be used instead.”

While traditionally a directory could be read with open() and read(), there is no guarantee that a modern system allows it.

Check errno after trying to read. You're probably getting EISDIR

Yes, I just checked and that is what I got. So I guess I can't try out the code from K&R2. In any case I have the functions I mentioned in dirent.h and they work with their code with almost no modification.