Redirecting STDIN, STDOUT, STDERR to /dev/null in C

Question

In Stevens\' UNIX Network Programming, he mentions redirecting stdin, stdout and stderr, which is needed when setting up a daemon. He does it with the following C code

Answer 1

Presumably file descriptors 0, 1, and 2 have already been closed when this code executes, and there are no other threads which might be allocating new file descriptors. In this case, since open is required to always allocate the lowest available file descriptor number, these three calls to open will yield file descriptors 0, 1, and 2, unless they fail.