I don't want to be toxic but why make a function to cast a char to an int? I was astounded when I briefly skimmed through the list. I hope this is not curriculum in education.
I don't see the one you're talking to on a brief skim, but there are several functions that deal with processing a file character by character. They generally use ints because they need a way to signal end of file and you can't do that with any value of a byte.