C++ cout

The cout object in C++ is an object of class ostream. It is used to display the output to the standard output device i.e. monitor. It is associated with the standard C output stream stdout.

cout declaration

extern ostream cout;

It is defined in <iostream> header file.

The cout object is ensured to be initialized during or before the first time an object of type ios_base::Init is constructed. After the cout object is constructed, it is tied to cin which means that any input operation on cin executes cout.flush().

The "c" in cout refers to "character" and 'out' means "output", hence cout means "character output". The cout object is used along with the insertion operator (<<) in order to display a stream of characters. The general syntax is:

cout << varName;

Or

cout << "Some String";

The extraction operator can be used more than once with a combination of variables, strings and manipulators (like endl):

cout << var1 << "Some String" << var2 << endl;

The cout object can also be used with other member functions such as put(), write(), etc. Some of the commonly used member functions are:

  • cout.put(char &ch): Displays the character stored by ch.
  • cout.write(char *str, int n): Displays the first n character reading from str.
  • cout.setf(option): Sets a given option. Commonly used options are left, right, scientific, fixed, etc.
  • cout.unsetf(option): Unsets a given option.
  • cout.precision(int n): Sets the decimal precision to n while displaying floating-point values. Same as cout << setprecision(n).

Example 1: cout with insertion operator:

#include <iostream>

using namespace std;

int main()
{
	int a,b;
	char str[] = "Hello Programmers";
	
	/* Single insertion operator */
	cout << "Enter 2 numbers - ";
	cin >> a >> b;
	cout << str;
	cout << endl;
	
	/* Multiple insertion operator */
	cout << "Value of a is " << a << endl << "Value of b is " << b;
	
	return 0;
}

When you run the program, a possible output will be:

Enter 2 numbers - 6 17
Hello Programmers
Value of a is 6
Value of b is 17

Example 2: cout with member function:

#include <iostream>

using namespace std;

int main()
{
	char str[] = "Do not interrupt me";
	char ch = 'm';
	
	cout.write(str,6);
	cout << endl;
	cout.put(ch);
	
	return 0;
}

When you run the program, a possible output will be:

Do not
m

Check these related library functions as well: