cout

Pre-defined stream

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

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.

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

//
// cout example one
//
#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 two
//
#include <iostream>

void main ( )
{
  using namespace std;

  char p[50];

  cin.getline(p,50);

  cout << p;   
}

//
// cout example three
//
#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 will greatly improve performance when C and C++ streams are not synchronized.

basic_ostream(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

©Copyright 1996, Rogue Wave Software, Inc.