Advanced Programming in the UNIX® Environment, Third Edition

3. File I/O

3.1. Introduction

We’ll start our discussion of the UNIX System by describing the functions available for file I/O—open a file, read a file, write a file, and so on. Most file I/O on a UNIX system can be performed using only five functions: open, read, write, lseek, and close. We then examine the effect of various buffer sizes on the read and write functions.

The functions described in this chapter are often referred to as unbuffered I/O, in contrast to the standard I/O routines, which we describe in Chapter 5. The term unbuffered means that each read or write invokes a system call in the kernel. These unbuffered I/O functions are not part of ISO C, but are part of POSIX.1 and the Single UNIX Specification.

Whenever we describe ...