is_void template in C++

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

Syntax:

template < class T > struct is_void;

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

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

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

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

Program 1:

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

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

// main program
int main()
{
    cout << boolalpha;
    cout << "is_void:"
         << '\n';
    cout << "void:"
         << is_void<void>::value
         << '\n';
    cout << "const void:"
         << is_void<const void>::value
         << '\n';
    cout << "int:"
         << is_void<int>::value
         << '\n';
    cout << "char:"
         << is_void<char>::value
         << '\n';

    return 0;
}

Output:

is_void:
void:true
const void:true
int:false
char:false

Program 2:

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

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

// main program
int main()
{
    cout << boolalpha;
    cout << "is_void:"
         << '\n';
    cout << "double:"
         << is_void<double>::value
         << '\n';
    cout << "float:"
         << is_void<float>::value
         << '\n';
    cout << "volatile void:"
         << is_void<volatile void>::value
         << '\n';
    cout << "const volatile void:"
         << is_void<const volatile void>::value
         << '\n';

    return 0;
}

Output:

is_void:
double:false
float:false
volatile void:true
const volatile void:true