Advanced Mac OS X Programming: The Big Nerd Ranch Guide

Buffered I/O

The system calls we have discussed here are generally called “unbuffered I/O.” There is a little bit of buffering that happens in the kernel, probably no more than a couple of disk blocks, so that a physical I/O is not performed for every byte read or written. But for the most part, what you read and write is what you get in terms of physical I/O. If you want to read in large chunks of data and process the data out of that buffer, you will have to do the work yourself: refilling the buffer when it gets low, remembering your place in the buffer, handling reading and writing, and so on. Not hard work, just tedious.

The Standard C I/O functions are known as “buffered I/O.” The library handles the details of buffer allocation I/O in ...