is_void template in C++

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

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

What is a void type in C++?

In simple words void means “empty” or “nothing”. When we declare a function as void then it is assumed that this function will return nothing.

We also declare void pointers, which are supposed to left unspecified. However, they must be referenced to another variable of other type, before the pointer is dereferenced. They can point to any object irrespective of their type, hence very useful for the programmers.

Syntax

template <class T>is_void;

Parameters

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

Return value

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

Example

Input: is_void<void>::value;
Output: True

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

Example

 Live Demo

#include <iostream>
#include <type_traits>
using namespace std;
int main() {
   cout << boolalpha;
   cout << "checking for is_void:";
   cout << "\nvoid:" << is_void<void>::value;
   cout << "\nconst void:" << is_void<const void>::value;
   cout << "\nint:" << is_void<int>::value;
   cout << "\nchar:" << is_void<char>::value;
   return 0;
}

Output

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

checking for is_void:
Void: true
Const void: true
Int: false
Char: false

Example

 Live Demo

#include <iostream>
#include <type_traits>
using namespace std;
int main() {
   cout << boolalpha;
   cout << "checking for is_void:";
   cout << "\nDouble:" << is_void<double>::value;
   cout << "\nFloat:" << is_void<float>::value;
   cout << "\nvolatile void:" << is_void<volatile void>::value;
   cout << "\nconst volatile void:" << is_void<const volatile void>::value;
   return 0;
}

Output

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

checking for is_void:
Double: false
Float: false
Volatile void: true
Cost volatile void: true