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 areleft
,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 ascout << 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()
.