![[Previous]](prev.gif) |
![[Contents]](contents.gif) |
![[Next]](next.gif) |
|
|
|
<iostream>Include the iostreams
standard header <iostream>
to declare objects that control reading from and writing to the
standard streams.
This is often the only header you
need include to perform input and output from a C++ program.
The objects fall into two groups:
cin,
cout,
cerr, and
clog are
byte oriented,
performing conventional byte-at-a-time transferswcin,
wcout,
wcerr, and
wclog are
wide oriented,
translating to and from the
wide characters
that the program manipulates internallyOnce you perform
certain operations
on a stream, such as the
standard input,
you cannot perform operations of a different orientation on
the same stream. Hence, a program cannot operate interchangeably on both
cin and
wcin, for example.
All the objects declared in this header share a peculiar
property -- you can assume they are
constructed before any
static objects you define, in a translation unit that includes
<iostreams>. Equally, you can assume that
these objects are not destroyed before the destructors for any
such static objects you define. (The output streams are, however,
flushed during program termination.)
Hence, you can safely read from
or write to the standard streams prior to program startup and
after program termination.
This guarantee is not universal, however. A static
constructor may call a function in another translation unit.
The called function cannot assume that the objects declared in
this header have been constructed, given the uncertain order
in which translation units participate in static construction.
To use these objects in such a context, you must first construct
an object of class
ios_base::Init,
as in:
#include <iostream>
void marker()
{ // called by some constructor
ios_base::Init unused_name;
cout << "called fun" << endl;
}
namespace std {
extern istream cin;
extern ostream cout;
extern ostream cerr;
extern ostream clog;
extern wistream wcin;
extern wostream wcout;
extern wostream wcerr;
extern wostream wclog;
};
cerrextern ostream cerr;
The object controls unbuffered insertions to the
standard error output
as a byte stream.
Once the object is constructed, the expression
cerr.flags() &
unitbuf is nonzero.
cinextern istream cin;
The object controls extractions from the
standard input
as a byte stream.
Once the object is constructed, the call
cin.tie() returns
&cout.
clogextern ostream clog;
The object controls buffered insertions to the standard error output as a byte stream.
coutextern ostream cout;
The object controls insertions to the standard output as a byte stream.
wcerrextern wostream wcerr;
The object controls unbuffered insertions to the
standard error output
as a wide stream.
Once the object is constructed, the expression
wcerr.flags() &
unitbuf is nonzero.
wcinextern wistream wcin;
The object controls extractions from the
standard input
as a wide stream.
Once the object is constructed, the call
wcin.tie() returns
&wcout.
wclogextern wostream wclog;
The object controls buffered insertions to the standard error output as a wide stream.
wcoutextern wostream wcout;
The object controls insertions to the standard output as a wide stream.
See also the Table of Contents and the Index.
Copyright © 1992-2002 by P.J. Plauger. All rights reserved.
|
|
|