8.1. The IO Classes

The IO types and objects that we’ve used so far manipulate char data. By default these objects are connected to the user’s console window. Of course, real programs cannot be limited to doing IO solely to or from a console window. Programs often need to read or write named files. Moreover, it can be convenient to use IO operations to process the characters in a string. Applications also may have to read and write languages that require wide-character support.

To support these different kinds of IO processing, the library defines a collection of IO types in addition to the istream and ostream types that we have already used. These types, which are listed in Table 8.1, are defined in three separate headers: iostream defines the basic types used to read from and write to a stream, fstream defines the types used to read and write named files, and sstream defines the types used to read and write in-memory strings.

Table 8.1. IO Library Types and Headers

To support languages that use wide characters, the library defines a set of types and objects that manipulate wchar_t data (§ 2.1.1, p. 32). The names of the wide-character versions begin with a w. For example, wcin, wcout, and wcerr are the wide-character objects that correspond to cin, cout, and cerr, respectively. The wide-character types and objects are defined in the same header as the plain char types. For example, the fstream header defines both the ifstream and wifstream types.