Chapter 15

Demystifying C++ I/O


  • What streams are
  • How to use streams for input and output of data
  • What the available standard streams are in the Standard Library

A program’s fundamental job is to accept input and produce output. A program that produces no output of any sort would not be very useful. All languages provide some mechanism for I/O, either as a built-in part of the language or through an OS-specific API. A good I/O system is both flexible and easy to use. Flexible I/O systems support input and output through a variety of devices, such as files and the user console. They also support reading and writing of different types of data. I/O is error-prone because data coming from a user can be incorrect or the underlying file system or other data source can be inaccessible. Thus, a good I/O system is also capable of handling error conditions.

If you are familiar with the C language, you have undoubtedly used printf() and scanf(). As I/O mechanisms, printf() and scanf() are certainly flexible. Through escape codes and variable placeholders, they can be customized to read in specially formatted data, or output any value that the formatting codes permit, which is currently limited to integer/character values, floating point values, and strings. However, printf() and scanf() falter on other measures of good I/O systems. They do not handle errors particularly well, they are not flexible enough to handle custom data types, and, worst of all in an object-oriented ...

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