>token</code> is interpreted as a
filesystem path.  It is assumed that this path denotes an operating
system pseudo-device which generates a stream of non-deterministic
random numbers.  The pseudo-device should never signal an error or
end-of-file.  Otherwise, <code>std::ios_base::failure</code> is
thrown.  By default, <code>random_device</code> uses the
<code>/dev/urandom</code> pseudo-device to retrieve the random
numbers.  Another option would be to specify the
<code>/dev/random</code> pseudo-device, whi