Practical C++ Programming, 2nd Edition

Chapter 16. File Input/Output

I am the heir of all the ages, in the foremost files of time.

—Tennyson

A file is a collection of related data. C++ treats a file as a series of bytes. Many files reside on disk; however, devices such as printers, magnetic tapes, and communication lines are also considered files.

This chapter discusses three different I/O packages. The first is the C++ I/O stream classes. This is the most commonly used I/O system and the one we’ve been using up to now. Next, we examine the raw I/O routines that give us direct access to the low-level I/O. Finally we look at the C I/O system. Although it is somewhat outdated, C I/O calls still appear in old code. Also, in some cases, the C-style I/O routines are superior to the ones provided with C++.

C++ File I/O

C++ file I/O is based on three classes: the istream class for input, the ostream class for output, and the iostream class for input/output. C++ refers to files as streams since it considers them a stream of bytes. Four class variables are automatically created when you start a program. These are listed in Table 16-1.

Table 16-1. Predefined I/O class variables

Variable	Use
cin	Console input (standard input)
cout	Console output (standard output)
cerr	Console error (standard error)
clog	Console log

These variables are defined in the standard include file <iostream> . Normally, std::cin is assigned to the keyboard and std::cout, std::cerr, and std::clog are assigned to the screen. Most operating systems allow you ...