Advanced Programming in the UNIX® Environment

ptg10805159

5

StandardI/O Library

5.1 Introduction

In this chapter, we describe the standardI/O library.This library is specified by the ISO

Cstandardbecause it has been implemented on many operating systems other than the

UNIX System. Additional interfaces aredefined as extensions to the ISO C standardby

the Single UNIX Specification.

The standardI/O library handles such details as buffer allocation and performing

I/O in optimal-sized chunks, obviating our need to worry about using the correct block

size (as in Section 3.9). This makes the library easy to use, but at the same time

introduces another set of problems if we’renot cognizant of what’s going on.

The standardI/O library was written by Dennis Ritchie around 1975. It was a major revision

of the Portable I/O library written by Mike Lesk. Surprisingly little has changed in the

standardI/O library after morethan 35 years.

5.2 Streams and FILEObjects

In Chapter 3, all the I/O routines centered on file descriptors. When a file is opened, a

file descriptor is returned, and that descriptor is then used for all subsequent I/O

operations. With the standardI/O library,the discussion centers onstreams.(Do not

confuse the standardI/O termstreamwith the STREAMS I/O system that is part of

System V and was standardized in the XSI STREAMS option in the Single UNIX

Specification, but is now marked obsolescent in SUSv4.) When we open or create a file

with the standardI/O library, we say that we have associated a stream with the file.

With the ASCII character set, a single character is represented by a single byte.With

international character sets, a character can be represented by morethan one byte.

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