is_reference Template in C++

C++Server Side ProgrammingProgramming

In this article we will be discussing the working, syntax and examples of std::is_reference template in C++ STL.

is_reference is a template which comes under <type_traits> header file. This template is used to check whether the given type T is a reference type or not.

This template is a combination of is_rvalue and is_lvalue and checks whether either if one is true, the result of is_reference will be also true.

What is a reference in C++?

A reference is an alias or another name of the already existing variable. A reference is different from pointer −

  • As we cannot set a reference as null but a pointer can be a null pointer.
  • Once a reference is initialised to an object it cant be changed. Pointers can be pointed to any other object at any time.
  • A reference must be initialised when created, where as pointer can be initialised later after creation.

A reference can be declared using an ampersand(&) symbol preceding the variable whom we want to refer.

Syntax

template <class T> is_reference;

Parameters

The template can have only parameter of type T, and check whether the given type is a reference type or not.

Return value

It returns a Boolean value, true if the given type is a reference type, and false if the given type is not a reference type.

Example

Input: is_reference<int>::value;
Output: False

Input: is_reference<int&>::value;
Output: True

Example

 Live Demo

#include <iostream>
#include <type_traits>
using namespace std;
class TP {
};
int main() {
   cout << boolalpha;
   cout << "Checking for is_reference: ";
   cout << "\n class TP : "<<is_reference<TP>::value;
   cout << "\n class TP&: "<<is_polymorphic<TP&>::value;
   cout << "\n class TP&&: "<<is_polymorphic<TP&&>::value;
   return 0;
}

Output

If we run the above code it will generate the following output −

Checking for is_reference:
class TP : false
class TP&: false
class TP&&: false

Example

 Live Demo

#include <iostream>
#include <type_traits>
using namespace std;
int main() {
   cout << boolalpha;
   cout << "Checking for is_reference: ";
   cout << "\n int: "<<is_reference<int>::value;
   cout << "\n int&: "<< is_reference <int&>::value;
   cout << "\n int&&: "<< is_reference <int&&>::value;
   // char
   cout << "\n char: "<<is_reference<char>::value;
   cout << "\n char&: "<< is_reference <char&>::value;
   cout << "\n char&&: "<< is_reference <char&&>::value;
   //float
   cout << "\n float: "<<is_reference<float>::value;
   cout << "\n float&: "<< is_reference <float&>::value;
   cout << "\n float&&: "<< is_reference <float&&>::value;
   //double
   cout << "\n double: "<<is_reference<double>::value;
   cout << "\n double&: "<< is_reference <double&>::value;
   cout << "\n double&&: "<< is_reference <double&&>::value;
   return 0;
}

Output

If we run the above code it will generate the following output −

Checking for is_reference:
int: false
int&: true
int&&: true
char: false
char&: true
char&&: true
float: false
float&: true
float&&: true
double: false
double&: true
double&&: true
raja
Published on 23-Mar-2020 07:58:01
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