what is exactly an EOF?

is EOF a special byte sequence that lies in the end of eve开发者_C百科ry file, or is it kinda exception(interrupt) that is notified by the kernel?

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Long ago on DOS machines it used to be indicated by ^Z, but nowadays it's the kernel reaching the end of the file and notifying the program when it tries to read further.

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I've used the ASCII EOF character to separate data files into a human-readable header followed by binary data. This allowed everything the mechanical engineers needed from a test to be kept in one file, while keeping it small enough to fit a floppy. (This was years ago!) The EOF character told most text display programs to stop. Anyone wanting a quick peek at the file header could just use a "print" command (is that what it was?) in a command shell.

Mostly these days, the EOF character isn't used in files, at least in the small part of the world I inhabit. Practically none of the ASCII control characters have any use any more, beside NUL, ESC and CR/LF.

EOF may serve some purpose in some streaming protocols, but that's outside my expertise so I leave it to others to address that.

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EOF is a special code returned by the C stdio library to denote that there's no more data to be read from a FILE. Different operating systems have their own way of recording the size/end of a file and their own way of returning that to a user program, which will be translated into an EOF return code by the C standard library implementation on that operating system.