is_reference Template in C++

The std::is_reference template of C++ STL is used to check whether the type is a reference type or not. It returns a boolean value showing the same.

Syntax:

template <class T > struct is_reference;

Parameter: This template accepts a single parameter T (Trait class) to check whether T is a reference type or not.

Return Value:This template returns a boolean value as shown below:

• True: if the type is a reference type.
• False: if the type is a non-reference type.

Below programs illustrate the std::is_reference template in C++ STL:

Program 1:

// C++ program to illustrate
// std::is_reference template

#include <iostream>
#include <type_traits>
using namespace std;

// main program
class gfg {
};

int main()
{
    cout << boolalpha;
    cout << "is_reference: "
         << '\n';
    cout << "gfg: "
         << is_reference<gfg>::value
         << '\n';
    cout << "gfg&: "
         << is_reference<gfg&>::value
         << '\n';
    cout << "gfg&&: "
         << is_reference<gfg&&>::value
         << '\n';

    return 0;
}

Output:

is_reference: 
gfg: false
gfg&: true
gfg&&: true

Program 2:

// C++ program to illustrate
// std::is_reference template

#include <iostream>
#include <type_traits>
using namespace std;

// main program
int main()
{
    cout << boolalpha;
    cout << "is_reference: "
         << '\n';
    cout << "int: "
         << is_reference<int>::value
         << '\n';
    cout << "int&: "
         << is_reference<int&>::value
         << '\n';
    cout << "int&&: "
         << is_reference<int&&>::value
         << '\n';
    cout << "char: "
         << is_reference<char>::value
         << '\n';
    cout << "char&: "
         << is_reference<char&>::value
         << '\n';
    cout << "char&&: "
         << is_reference<char&&>::value
         << '\n';

    return 0;
}

Output:

is_reference: 
int: false
int&: true
int&&: true
char: false
char&: true
char&&: true

Program 3:

// C++ program to illustrate
// std::is_reference template

#include <iostream>
#include <type_traits>
using namespace std;

// main program
int main()
{

    cout << boolalpha;
    cout << "is_reference: "
         << '\n';
    cout << "float: "
         << is_reference<float>::value
         << '\n';
    cout << "float&: "
         << is_reference<float&>::value
         << '\n';
    cout << "float&&: "
         << is_reference<float&&>::value
         << '\n';
    cout << "double: "
         << is_reference<double>::value
         << '\n';
    cout << "double&: "
         << is_reference<double&>::value
         << '\n';
    cout << "double&&: "
         << is_reference<double&&>::value
         << '\n';

    return 0;
}

Output:

is_reference: 
float: false
float&: true
float&&: true
double: false
double&: true
double&&: true