Standard Input and Output Objects

The library defines four IO objects. To handle input, we use an object of type istream named cin (pronounced see-in). This object is also referred to as the standard input. For output, we use an ostream object named cout (pronounced see-out). This object is also known as the standard output. The library also defines two other ostream objects, named cerr and clog (pronounced see-err and see-log, respectively). We typically use cerr, referred to as the standard error, for warning and error messages and clog for general information about the execution of the program.

Ordinarily, the system associates each of these objects with the window in which the program is executed. So, when we read from cin, data are read from the window in which the program is executing, and when we write to cout, cerr, or clog, the output is written to the same window.