Using the "file length" as opposed to the "EOF indicator" is like how strings can either be represented as pointer to a contiguous sequence of `char` ending wit

Using the "file length" as opposed to the "EOF indicator" is like how strings can either be represented as pointer to a contiguous sequence of `char` ending with a NULL byte, or as a tuple of (length, pointer), without the needed NULL byte. One gives a priori information the other a posteriori.