The most important thing to keep in mind whenever we're talking about file I/O is that everything I/O-related in C and C++ is built on top of the POSIX standard. POSIX is a very low-level specification, almost at the level of Linux system calls, that has quite a bit of overlap with the C and C++ standards for I/O; and, if you don't understand the gist of the POSIX layer, you'll have a very hard time understanding the concepts that come later.
Bear in mind that technically, none of what follows is standard C++! It is, rather, valid C++ that conforms to a non-C++ standard: the POSIX standard. In practice, this means that it'll work on any operating system except Windows, and may even work on modern Windows systems via the ...
