Inserters and extractors

In the iostreams library, two operators have been overloaded to make the use of iostreams easy. The operator << is often referred to as an inserter for iostreams, and the operator >> is often referred to as an extractor.

A stream is an object that formats and holds bytes. You can have an input stream (istream) or an output stream (ostream). There are different types of istreams and ostreams: ifstreams and ofstreams for files, istrstreams , and ostrstreams for char* memory (in-core formatting), and istringstreams & ostringstreams for interfacing with the Standard C++ string class. All these stream objects have the same interface, regardless of whether you’re working with a file, standard I/O, a piece of memory or a string object. The single interface you learn also works for extensions added to support new classes.

If a stream is capable of producing bytes (an istream), you can get information from the stream using an extractor. The extractor produces and formats the type of information that’s expected by the destination object. To see an example of this, you can use the cin object, which is the iostream equivalent of stdin in C, that is, redirectable standard input. This object is pre-defined whenever you include the iostream.h header file. (Thus, the iostream library is automatically linked with most compilers.)

int i; cin >> i;

float f; cin >> f;

char c; cin >> c;

char buf[100]; cin >> buf;

There’s an overloaded operator >> for every data type you can use as the right-hand argument of >> in an iostream statement. (You can also overload your own, which you’ll see in a later chapter.)

To find out what you have in the various variables, you can use the cout object (corresponding to standard output; there’s also a cerr object corresponding to standard error) with the inserter <<:

cout << "i = "; cout << i;

cout << "\n"; cout << "f = "; cout << f;

cout << "\n";

Chapter 14: Templates & Container Classes

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