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Showing content from https://cplusplus.com/reference/type_traits/is_fundamental/ below:

class template

<type_traits>

std::is_fundamental

template <class T> struct is_fundamental;

Is fundamental type

Trait class that identifies whether T is a fundamental type.

It inherits from integral_constant as being either true_type or false_type, depending on whether T is one of the following types:

fundamental arithmetic types integral types bool char char16_t char32_t wchar_t signed char short int int long int long long int unsigned char unsigned short int unsigned int unsigned long int unsigned long long int floating point types float double long double void void null pointer std::nullptr_t

All fundamental types, along with all their aliases (like those in cstdint), are considered fundamental types by this class, including their const and volatile qualified variants.

Enums, along with pointers, references, classes and functions are not considered fundamental types in C++.

This is a compound type trait defined with the same behavior as:

template<class T>
struct is_fundamental : std::integral_constant < bool,
         is_integral<T>::value || is_floating_point<T>::value || is_void<T>:: value ||
         is_same<nullptr_t, typename remove_cv<T>::type>::value> {};

Template parameters

T: A type.

Member types Inherited from integral_constant:

Member constants Inherited from integral_constant:
member constant definition value either true or false
Member functions Inherited from integral_constant:

operator bool: Returns value (public member function)

Example

// is_fundamental example
#include <iostream>
#include <type_traits>

int main() {
  std::cout << std::boolalpha;
  std::cout << "is_fundamental:" << std::endl;
  std::cout << "unsigned: " << std::is_fundamental<unsigned>::value << std::endl;
  std::cout << "float: " << std::is_fundamental<float>::value << std::endl;
  std::cout << "float*: " << std::is_fundamental<float*>::value << std::endl;
  std::cout << "decltype(nullptr): " << std::is_fundamental<decltype(nullptr)>::value << std::endl;
  return 0;
}

Output:

is_fundamental:
unsigned: true
float: true
float*: false
decltype(nullptr): true