The include header <iostream> declared input and output stream objects. The declared objects are associated with the standard C streams provided for by the functions in <cstdio>.

Overview of Standard Input and Output Stream Objects.

The ANSI/ISO standard calls for predetermined objects for standard input, output, logging and error reporting. This is initialized for normal and wide character formats.

Header <iostream>

Declaration of standard objects

Prototype:

Header <iostream>

namespace std{

extern istream cin;

extern ostream cout;

extern ostream cerr;

extern ostream clog;

extern wistream wcin;

extern wostream wcout;

extern wostream cerr;

extern wostream wclog;

}

Additional topics are:

• "27.3.1 Narrow stream objects"
• "27.3.2 Wide stream objects"

Stream Buffering

All streams are buffered (by default) except cerr and wcerr.

NOTE

You can change the buffering characteristic of a stream with:

  cout.setf(ios_base::unitbuf);   or
  cerr.unsetf(ios_base::unitbuf);

27.3.1 Narrow stream objects

Narrow stream objects provide unbuffered input and output associated with standard input and output declared in <cstdio>.

istream cin

An unbuffered input stream.

Prototype:

istream cin;

The object cin controls input from an unbuffered stream buffer associated with stdin declared in <cstdio>. After cin is initialized cin.tie() returns cout.

Return:

An istream object;

ostream cout

An unbuffered output stream.

Prototype:

ostream cout;

The object cout controls output to an unbuffered stream buffer associated with stdout declared in <cstdio>.

Return:

An ostream object;

ostream cerr

Controls output to an unbuffered stream.

Prototype:

ostream cerr;

The object cerr controls output to an unbuffered stream buffer associated with stderr declared in <cstdio>. After err is initialized, err.flags() and unitbuf is nonzero.

Return:

An ostream object;

ostream clog

Controls output to a stream buffer.

Prototype:

ostream clog;

The object clog controls output to a stream buffer associated with cerr declared in <cstdio>.

Return:

An ostream object;

27.3.2 Wide stream objects

Narrow stream objects provide unbuffered input and output associated with standard input and output declared in <cstdio>.

istream wcin

An unbuffered input stream.

Prototype:

wistream wcin;

The object win controls input from an unbuffered stream buffer associated with stdin declared in <cstdio>. After cin is initialized win.tie() returns wout.

Return:

An wistream object;

ostream wcout

An unbuffered output stream.

Prototype:

wostream wcout;

The object cout controls output to an unbuffered stream buffer associated with stdout declared in <cstdio>.

Return:

An wostream object;

wostream wcerr

Controls output to an unbuffered stream.

Prototype:

wostream wcerr;

The object werr controls output to an unbuffered stream buffer associated with stderr declared in <cstdio>. After werr is initialized, werr.flags() and unitbuf is nonzero.

Return:

An ostream object;

wostream wlcog

Controls output to a stream buffer.

Prototype:

wostream wclog;

The object wlog controls output to a stream buffer associated with cerr declared in <cstdio>.

Return:

An ostream object