<iostream>
Declares objects that control reading from and writing to the standard streams. This include is often the only header you need to do input and output from a C++ program.
#include <iostream>
Note
The <iostream>
library uses the #include <ios>
, #include <streambuf>
, #include <istream>
, and #include <ostream>
statements.
The objects fall into two groups:
cin
,cout
,cerr
, andclog
are byte oriented, doing conventional byte-at-a-time transfers.wcin
,wcout
,wcerr
, andwclog
are wide oriented, translating to and from the wide characters that the program manipulates internally.
Once you do certain operations on a stream, such as the standard input, you can't do operations of a different orientation on the same stream. Therefore, a program can't operate interchangeably on both cin
and wcin
, for example.
All the objects declared in this header share a peculiar property — you can assume they're constructed before any static objects you define, in a translation unit that includes <iostream>
. Equally, you can assume that these objects aren't destroyed before the destructors for any such static objects you define. (The output streams are, however, flushed during program termination.) Therefore, you can safely read from or write to the standard streams before program startup and after program termination.
This guarantee isn't universal, however. A static constructor may call a function in another translation unit. The called function can't 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
.
Name | Description |
---|---|
cerr |
Specifies the cerr global stream. |
cin |
Specifies the cin global stream. |
clog |
Specifies the clog global stream. |
cout |
Specifies the cout global stream. |
wcerr |
Specifies the wcerr global stream. |
wcin |
Specifies the wcin global stream. |
wclog |
Specifies the wclog global stream. |
wcout |
Specifies the wcout global stream. |
The object cerr
controls output to a stream buffer associated with the object stderr
, declared in <cstdio>
.
extern ostream cerr;
An ostream
object.
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, and cerr.tie() == &cout
. For more details, see cerr.flags
and unitbuf
.
// iostream_cerr.cpp
// compile with: /EHsc
#include <iostream>
#include <fstream>
using namespace std;
void TestWide( )
{
int i = 0;
wcout << L"Enter a number: ";
wcin >> i;
wcerr << L"test for wcerr" << endl;
wclog << L"test for wclog" << endl;
}
int main( )
{
int i = 0;
cout << "Enter a number: ";
cin >> i;
cerr << "test for cerr" << endl;
clog << "test for clog" << endl;
TestWide( );
}
Specifies the cin
global stream.
extern istream cin;
An istream
object.
The object controls extractions from the standard input as a byte stream. Once the object is constructed, the call cin.tie
returns &cout
.
In this example, cin
sets the fail bit on the stream when it comes across non-numeric characters. The program clears the fail bit and strips the invalid character from the stream to continue.
// iostream_cin.cpp
// compile with: /EHsc
#include <iostream>
using namespace std;
int main()
{
int x;
cout << "enter choice:";
cin >> x;
while (x < 1 || x > 4)
{
cout << "Invalid choice, try again:";
cin >> x;
// not a numeric character, probably
// clear the failure and pull off the non-numeric character
if (cin.fail())
{
cin.clear();
char c;
cin >> c;
}
}
}
2
Specifies the clog
global stream.
extern ostream clog;
An ostream
object.
The object controls buffered insertions to the standard error output as a byte stream.
See cerr
for an example of using clog
.
Specifies the cout
global stream.
extern ostream cout;
An ostream
object.
The object controls insertions to the standard output as a byte stream.
See cerr
for an example of using cout
.
Specifies the wcerr
global stream.
extern wostream wcerr;
A wostream
object.
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. For more details, see wcerr.flags
and unitbuf
.
See cerr
for an example of using wcerr
.
Specifies the wcin
global stream.
extern wistream wcin;
A wistream
object.
The object controls extractions from the standard input as a wide stream. Once the object is constructed, the call wcin.tie
returns &wcout
.
See cerr
for an example of using wcin
.
Specifies the wclog
global stream.
extern wostream wclog;
A wostream
object.
The object controls buffered insertions to the standard error output as a wide stream.
See cerr
for an example of using wclog
.
Specifies the wcout
global stream.
extern wostream wcout;
A wostream
object.
The object controls insertions to the standard output as a wide stream.
See cerr
for an example of using wcout
.
CString
instances in a wcout
statement must be cast to const wchar_t*
, as shown in the following example.
CString cs("meow");
wcout <<(const wchar_t*) cs <<endl;
For more information, see Basic CString Operations.
Header Files Reference
Thread Safety in the C++ Standard Library
iostream Programming
iostreams Conventions