When creating a program using C++ which symbol is used for the insertion operator?

In this tutorial, we will learn about the C++ cout object with the help of examples.

The cout object is used to display the output to the standard output device. It is defined in the iostream header file.

Example

#include <iostream>

using namespace std;

int main() {
  int a = 24;
	
  // print variable
  cout << "Value of a is " << a;
	
  return 0;
}

// Output: Value of a is 24

cout Syntax

The syntax of the cout object is:

cout << var_name;

Or

cout << "Some String";

Here,

• << is the insertion operator
• var_name is usually a variable, but can also be an array element or elements of containers like vectors, lists, maps, etc.

cout with Insertion Operator

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. For example,

int var1 = 25, var2 = 50;

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

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

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

Example 1: cout with Insertion Operator

#include <iostream>
using namespace std;

int main() {
  int a,b;
  string str = "Hello Programmers";
	
  // single insertion operator
  cout << "Enter 2 numbers - ";

  cin >> a >> b;

  cout << str;
  cout << endl;
	
  // multiple insertion operators
  cout << "Value of a is " << a << endl << "Value of b is " << b;

  return 0;
}

Output

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

cout with Member Functions

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 2: cout with Member Function

#include <iostream>

using namespace std;

int main() {
  string str = "Do not interrupt me";
  char ch = 'm';
	
  // use cout with write()
  cout.write(str,6);

  cout << endl;

  // use cout with put()
  cout.put(ch);
	
  return 0;
}

Output

Do not
m

cout Prototype

The prototype of cout as defined in the iostream header file is:

extern ostream cout;

The cout object in C++ is an object of class ostream. It is associated with the standard C output stream stdout.

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().

I'm wondering if there is a standard name for the "<<" and ">>" operators? This is mostly in the context of teaching C++ and using those operators as part of stream input/output. If I need to read code or prompt for student responses (such as cout << "Hello";), I'm not sure how to verbalize those symbols. Is there a convention when reading them out loud?

Improved version of this question: How do you read the "<<" and ">>" symbols out loud?

asked Mar 11, 2017 at 3:06

7

When not overloaded, left-shift and right-shift and some people call them that even when used with streams, but insertion and extraction is a lot more common in that context. They are also sometimes informally called put to and get from. IIRC, Stroustrup favoured that last form.

answered Mar 11, 2017 at 3:10

Jon HannaJon Hanna

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3

According to cplusplus.com's documentation:

This operator (<<) applied to an output stream is known as insertion operator.

...

And from the same website

This operator (>>) applied to an input stream is known as extraction operator.

...

answered Mar 11, 2017 at 3:11

nbronbro

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In his book "The C++ Programming Language", C++11, bjarne stroustrup has called << "put to" and >> "get from".

Hope this helps

answered Mar 11, 2017 at 3:13

Son NguyenSon Nguyen

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<< is the insertion operator. Note when you write

cout << "Some text";

The arrows are pointing to the stream. You're inserting the text into the stream.

>> is the extraction operator. When you write

cin >> some_var;

You're extracting a value from the stream.

answered Mar 11, 2017 at 3:12

CarcigenicateCarcigenicate

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2

Those are officially bitwise shift operators (e.g., 1 << 3 is 8), but they're often overloaded as stream insertion/stream extraction operators (as in the cout example you gave).

answered Mar 11, 2017 at 3:10

3

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