std::is_same (3) - Linux Manuals

std::is_same: std::is_same

NAME

std::is_same - std::is_same

Synopsis

Defined in header <type_traits>
template< class T, class U > (since C++11)
struct is_same;

If T and U name the same type (including const/volatile qualifications), provides the member constant value equal to true. Otherwise value is false.
Commutativity is satisfied, i.e. for any two types T and U, is_same<T, U>::value == true if and only if is_same<U, T>::value == true.

Helper variable template

template< class T, class U > (since C++17)
inline constexpr bool is_same_v = is_same<T, U>::value;

Inherited from std::integral_constant

Member constants

value true if T and U is the same type , false otherwise
         (public static member constant)
[static]

Member functions

              converts the object to bool, returns value
operator bool (public member function)

operator() returns value
              (public member function)
(C++14)

Member types

Type Definition
value_type bool
type std::integral_constant<bool, value>

Possible implementation

  template<class T, class U>
  struct is_same : std::false_type {};

  template<class T>
  struct is_same<T, T> : std::true_type {};

Example

// Run this code

  #include <iostream>
  #include <type_traits>
  #include <cstdint>

  void print_separator()
  {
      std::cout << "-----\n";
  }

  int main()
  {
      std::cout << std::boolalpha;

      // some implementation-defined facts
      std::cout << std::is_same<int, std::int32_t>::value << '\n';
      // usually true if 'int' is 32 bit
      std::cout << std::is_same<int, std::int64_t>::value << '\n';
      // possibly true if ILP64 data model is used

      print_separator();

      // 'float' is never an integral type
      std::cout << std::is_same<float, std::int32_t>::value << '\n'; // false

      print_separator();

      // 'int' is implicitly 'signed'
      std::cout << std::is_same<int, int>::value << "\n"; // true
      std::cout << std::is_same<int, unsigned int>::value << "\n"; // false
      std::cout << std::is_same<int, signed int>::value << "\n"; // true

      print_separator();

      // unlike other types, 'char' is neither 'unsigned' nor 'signed'
      std::cout << std::is_same<char, char>::value << "\n"; // true
      std::cout << std::is_same<char, unsigned char>::value << "\n"; // false
      std::cout << std::is_same<char, signed char>::value << "\n"; // false
  }

Possible output:

  true
  false
  -----
  false
  -----
  true
  false
  true
  -----
  true
  false
  false