Advanced Programming in the UNIX® Environment

ptg10805159

18

Terminal I/O

18.1 Introduction

The handling of terminal I/O is a messy area, regardless of the operating system. The

UNIX System is no exception. The manual page for terminal I/O is usually one of the

longest in most editions of the programmer ’s manuals.

With the UNIX System, a schism formed in the late 1970s when System III

developed a different set of terminal routines from those of Version 7. The System III

style of terminal I/O continued through System V,and the Version 7 style became the

standardfor the BSD-derived systems. As with signals, this difference between the two

worlds has been conquered by POSIX.1. In this chapter, we look at all the POSIX.1

terminal functions and some of the platform-specific additions.

Part of the complexity of the terminal I/O system occurs because people use

terminal I/O for so many different things: terminals, hard-wired lines between

computers, modems, printers, and so on.

18.2 Overview

Te rminal I/O has two modes:

1. Canonical mode input processing. In this mode, terminal input is processed as
   lines. The terminal driver returns at most one line per read request.


2. Noncanonical mode input processing. The input characters arenot assembled
   into lines.

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