cout

Pre-defined stream

• Summary
• Data Type and Member Function Indexes
• Synopsis
• Description
• Formatting
• Description
• Default Values
• Example
• Warnings
• See Also
• Standards Conformance

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

None

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

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.

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( )

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

//
// 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;
    }
}

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.

basic_ostream(3C++), 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

ANSI X3J16/ISO WG21 Joint C++ Committee