C++ Primer Plus

                 " the full moon glowed brilliantly. ";

    istringstream instr(lit);   // use buf for input

    string word;

    while (instr >> word)       // read a word a time

        cout << word << endl;

    return 0;

}

Here is the output of the program in Listing 17.22:

It

was

a

dark

and

stormy

day,

and

the

full

moon

glowed

brilliantly.

In short, the istringstream and ostringstream classes give you the power of the istream and ostream class methods to manage character data stored in strings.

Summary

A stream is a flow of bytes into or out of a program. A buffer is a temporary holding area in memory that acts as an intermediary between a program and a file or other I/O devices. Information can be transferred between a buffer and a file, using large chunks of data of the size most efficiently handled by devices such as disk drives. And information can be transferred between a buffer and a program in a byte-by-byte flow that often is more convenient for the processing done in a program. C++ handles input by connecting a buffered stream to a program and to its source of input. Similarly, C++ handles output by connecting a buffered stream to a program and to its output target. The iostream and fstream files constitute an I/O class library that defines a rich set of classes for managing streams. C++ programs that include the iostream file automatically open eight streams, managing them with eight objects. The cin object manages the standard input stream, which, by default, connects to the standard input device, typically a keyboard. The cout object manages the standard output stream, which, by default, connects to the standard output device, typically a monitor. The cerr and clog objects manage unbuffered and buffered streams connected to the standard error device, typically a monitor. These four objects have four wide character counterparts, named wcin, wcout, wcerr, and wclog.

The I/O class library provides a variety of useful methods. The istream class defines versions of the extraction operator (>>) that recognize all the basic C++ types and that convert character input to those types. The get() family of methods and the getline() method provide further support for single-character input and for string input. Similarly, the ostream class defines versions of the insertion operator (<<) that recognize all the basic C++ types and that convert them to suitable character output. The put() method provides further support for single-character output. The wistream and wostream classes provide similar support for wide characters.

You can control how a program formats output by using ios_base class methods and by using manipulators (functions that can be concatenated with insertion) defined in the iostream and iomanip files. These methods and manipulators let you control the number base, the field width, the number of decimal places displayed, the system used to display floating-point values, and other elements.

The fstream file provides class definitions that extend the iostream methods to file I/O. The ifstream class derives from the istream class. By associating an ifstream object with a file, you can use all the istream methods for reading the file. Similarly, associating an ofstream object with a file lets you use the ostream methods to write to a file. And associating an fstream object with a file lets you employ both input and output methods with the file.

To associate a file with a stream, you can provide the filename when initializing a file stream object or you can first create a file stream object and then use the open() method to associate the stream with a file. The close() method terminates the connection between a stream and a file. The class constructors and the open() method take an optional second argument that provides the file mode. The file mode determines such things as whether the file is to be read and/or written to, whether opening a file for writing truncates it, whether attempting to open a non-existent file is an error, and whether to use the binary or text mode.

A text file stores all information in character form. For example, numeric values are converted to character representations. The usual insertion and extraction operators, along with get() and getline(), support this mode. A binary file stores all information by using the same binary representation the computer uses internally. Binary files store data, particularly floating-point values, more accurately and compactly than text files, but they are less portable. The read() and write() methods support binary input and output.

The seekg() and seekp() functions provide C++ random access for files. These class methods let you position a file pointer relative to the beginning of a file, relative to the end, or relative to the current position. The tellg() and tellp() methods report the current file position.