How does fchdir work?

Question

In it's main page it says:

fchdir() is identical to chdir(); the only difference is that the directory is given as an open file descriptor.

And the prototype is given as following:

int chdir(const char *path);
int fchdir(int fd);

My question is how can a directory be passed as a file descriptor? Do directories also have a corresponding descriptor like files?

Answer 1

Do directories also have a corresponding descriptor like files?

Yes. The Unix philosophy(and Linux) is to treat everything as a stream of bytes. So yes, you can do open(2) on a directory and get its file descriptor. Not only directories but sockets, pipes and devices can also be opened using open(2) system call and do operations on it as though it's a file.