The author of this software is David M. Gay.

Copyright (c) 1991 by AT&T.

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2 Operators and Default Streams

The STL port library,implements the standard input and output facilities for C++. These facilities are analogous with those defined by the C `stdio' functions. Although these definitions come from a library, rather than being part of the "core language", they are sufficiently central to be specified in the latest working papers for C++.

Use the insertion (<<) and extraction (>>) operators defined in this library for basic input and output operations. These operators are often used in conjunction with three streams that are open by default:

Variable: ostream cout

The standard output stream, analogous to the C stdout.

Variable: istream cin

The standard input stream, analogous to the C stdin.

Variable: ostream cerr

An alternative output stream for errors, analogous to the C stderr.

For example, this bare-bones C++ version of the traditional "Hello World" program uses << and cout:

#include <iostream.h>

int main(int argc, char **argv)
{
  cout << "Hello World!\n";
  return 0;
}

Although, the use of these operators is all right in throwaway code, it is not good programming practice. A robust code checks the state of the input and output streams between operations (for example, using the method good) see Checking the state of a stream. To adjust maximum input or output field widths, use manipulators like setw or setprecision.

Operator: ostream <<

Writes output to an open output stream of class ostream. Defined by this library on any object of a C++ primitive type, and on other classes of the library. The definition can be overloaded for any of the user's own application classes.

Returns a reference to the implied argument *this (the open stream it writes on), permitting statements like:

cout << "The value of i is " << i << "\n";

Operator: istream >>

Reads input from an open input stream of class istream. Defined by this library on primitive numeric, pointer, and string types; the definition can be expanded for any of the user's own application classes.

Returns a reference to the implied argument *this (the open stream it reads), permitting multiple inputs in one statement.