Standard C++ Library
Copyright 1998, Rogue Wave Software, Inc.

 

NAME

 
cout
 
 - Controls output to a stream buffer associated with the object stdout declared in <cstdio>. 
 
 
 

SYNOPSIS

 
 
#include <iostream>
extern ostream cout;
ostream cout;
 
 
 

DESCRIPTION

 
 
The object cout controls output to a stream buffer associated with the object stdout declared in <cstdio>. By default the standard C and C++ streams are synchronized, but performance improvement can be achieved by using the ios_base member function synch_with_stdio to desynchronize them. 
 
After the object cin is initialized, cin.tie() returns &cout, which implies that cin and cout are synchronized. 
 
 
 

FORMATTING

 
 
The formatting is done through member functions or manipulators.
 
MANIPULATORS  MEMBER FUNCTIONS
 
 
showpos setf(ios_base::showpos)
 
 
 
noshowpos unsetf(ios_base::showpos)
 
 
 
showbase setf(ios_base::showbase)
 
 
 
noshowbase unsetf(ios_base::showbase)
 
 
 
uppercase setf(ios_base::uppercase)
 
 
 
nouppercase unsetf(ios_base::uppercase)
 
 
 
showpoint setf(ios_base::showpoint)
 
 
 
noshowpoint unsetf(ios_base::showpoint)
 
 
 
boolalpha setf(ios_base::boolalpha)
 
 
 
noboolalpha unsetf(ios_base::boolalpha)
 
 
 
unitbuf setf(ios_base::unitbuf)
 
 
 
nounitbuf unsetf(ios_base::unitbuf)
 
 
 
internal setf(ios_base::internal,
                 ios_base::adjustfield)
 
 
 
left setf(ios_base::left,
             ios_base::adjustfield)
 
 
 
right setf(ios_base::right,
              ios_base::adjustfield)
 
 
 
dec setf(ios_base::dec,
            ios_base::basefield)
 
 
 
hex setf(ios_base::hex,
            ios_base::basefield)
 
 
 
oct setf(ios_base::oct,
            ios_base::basefield)
 
 
 
fixed setf(ios_base::fixed,
              ios_base::floatfield)
 
 
 
scientific setf(ios_base::scientific,
                   ios_base::floatfield)
 
 
 
resetiosflags
  (ios_base::fmtflags flag) setf(0,flag)
 
 
 
setiosflags
  (ios_base::fmtflags flag) setf(flag)
 
 
 
setbase(int base) see above
 
 
 
setfill(char_type c) fill(c)
 
 
 
setprecision(int n) precision(n)
 
 
 
setw(int n) width(n)
 
 
endl
 
ends
 
flush flush( )
 
 

DESCRIPTION

 

showpos   Generates a + sign in non-negative generated numeric output. 

 

showbase   Generates a prefix indicating the numeric base of generated integer output

 

uppercase   Replaces certain lowercase letters with their uppercase equivalents in generated output

 

showpoint   Generates a decimal-point character unconditionally in generated floating-point output

 

boolalpha   Inserts and extracts bool type in alphabetic format

 

unitbuf   Flushes output after each output operation

 

internal   Adds fill characters at a designated internal point in certain generated output. If no such point is designated, it’s identical to right. 

 

left   Adds fill characters on the right (final positions) of certain generated output

 

right   Adds fill characters on the left (initial positions) of certain generated output

 

dec   Converts integer input or generates integer output in decimal base

 

hex   Converts integer input or generates integer output in hexadecimal base

 

oct   Converts integer input or generates integer output in octal base

 

fixed   Generates floating-point output in fixed-point notation

 

scientific   Generates floating-point output in scientific notation

 
resetiosflags

(ios_base::fmtflags flag)Resets the fmtflags field flag

 
setiosflags

(ios_base::fmtflags flag)Sets up the flag flag

 

setbase(int base)   Converts integer input or generates integer output in base base. The parameter base can be 8, 10 or 16. 

 

setfill(char_type c)   Sets the character used to pad (fill) an output conversion to the specified field width

 

setprecision(int n)   Sets the precision (number of digits after the decimal point) to generate on certain output conversions

 

setw(int n)   Sets the field with (number of characters) to generate on certain output conversions

 
 
 
 

showpos   Generates a + sign in non-negative generated numeric output. 

 

showbase   Generates a prefix indicating the numeric base of generated integer output

 

uppercase   Replaces certain lowercase letters with their uppercase equivalents in generated output

 

showpoint   Generates a decimal-point character unconditionally in generated floating-point output

 

boolalpha   Inserts and extracts bool type in alphabetic format

 

unitbuf   Flushes output after each output operation

 

internal   Adds fill characters at a designated internal point in certain generated output. If no such point is designated, it’s identical to right. 

 

left   Adds fill characters on the right (final positions) of certain generated output

 

right   Adds fill characters on the left (initial positions) of certain generated output

 

dec   Converts integer input or generates integer output in decimal base

 

hex   Converts integer input or generates integer output in hexadecimal base

 

oct   Converts integer input or generates integer output in octal base

 

fixed   Generates floating-point output in fixed-point notation

 

scientific   Generates floating-point output in scientific notation

 
resetiosflags

(ios_base::fmtflags flag)Resets the fmtflags field flag

 
setiosflags

(ios_base::fmtflags flag)Sets up the flag flag

 

setbase(int base)Converts integer input or generates integer output in base base. The parameter base can be 8, 10 or 16. 

 

setfill(char_type c)   Sets the character used to pad (fill) an output conversion to the specified field width

 

setprecision(int n)   Sets the precision (number of digits after the decimal point) to generate on certain output conversions

 

setw(int n)   Sets the field with (number of characters) to generate on certain output conversions

 

endl   Inserts a newline character into the output sequence and flush the output buffer. 

 

ends   Inserts a null character into the output sequence. 

 

flush   Flush the output buffer. 

 
 

DEFAULT VALUES

 
 
 
precision()            6
width()                0
fill()                 the space character
flags()                skipws | dec
getloc()               locale::locale()
 
 
 

EXAMPLE

 
 
 
//
// cout example #1
//
#include<iostream>
#include<iomanip>
 
void main ( )
{

using namespace std;

 

int i;
float f;

 
// read an integer and a float from stdin

cin >> i >> f;

// output the integer and goes at the line

cout << i << endl;

 

// output the float and goes at the line

cout << f << endl;

 

// output i in hexa

cout << hex << i << endl;

 

// output i in octal and then in decimal

cout << oct << i << dec << i << endl;

 

// output i preceded by its sign

cout << showpos << i << endl;

 

// output i in hexa

cout << setbase(16) << i << endl;

 

// output i in dec and pad to the left with character
// @ until a width of 20
// if you input 45 it outputs 45@@@@@@@@@@@@@@@@@@

cout << setfill(’@’) << setw(20) << left << dec << i;
cout << endl;

 

// output the same result as the code just above
// but uses member functions rather than manipulators

cout.fill(’@’);
cout.width(20);
cout.setf(ios_base::left, ios_base::adjustfield);
cout.setf(ios_base::dec, ios_base::basefield);
cout << i << endl;

 

// outputs f in scientific notation with
// a precision of 10 digits

cout << scientific << setprecision(10) << f << endl;

 

// change the precision to 6 digits
// equivalents to cout << setprecision(6);

cout.precision(6);

 

// output f and goes back to fixed notation

cout << f << fixed << endl;

 
}
//
// cout example #2
//
#include <iostream>
 
void main ( )
{

using namespace std;

 

char p[50];

 

cin.getline(p,50);

 

cout << p;

}
//
// cout example #3
//
#include <iostream>
#include <fstream>
 
void main ( )
{

using namespace std;

 

// open the file "file_name.txt"
// for reading

ifstream in("file_name.txt");

 
// output the all file to stdout

if ( in )

cout << in.rdbuf();

else

{

cout << "Error while opening the file";
cout << endl;

}

}
 
 
 

WARNINGS

 
 
Keep in mind that the manipulator endl flushes the stream buffer. Therefore it is recommended to use ‘\n’ if your only intent is to go at the line. It greatly improves performance when C and C++ streams are not synchronized. 
 
If your compiler does not support namespaces, then you do not need the using declaration for std. 
 
 
 

SEE ALSO

 
 
basic_ostream(3C++), basic_iostream(3C++), basic_filebuf(3C++), cin(3C++), cerr(3C++), clog(3C++), wcin(3C++), wcout(3C++), wcerr(3C++), wclog(3C++), iomanip(3C++)
 
Working Paper for Draft Proposed International Standard for Information Systems--Programming Language C++, Section 27.3.1
 
 
 

STANDARDS CONFORMANCE

 
 
ANSI X3J16/ISO WG21 Joint C++ Committee
 

Rogue Wave Software  —  Last change: 02 Apr 1998