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

If T and U name the same type (taking into account 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.

The behavior of a program that adds specializations for is_same or is_same_v (since C++17) is undefined.

Helper variable template

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

Inherited from std::integral_constant

Member constants

true if T and U are the same type , false otherwise
(public static member constant)

Member functions

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

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 {};


#include <iostream>
#include <type_traits>
#include <cstdint>
void print_separator()
    std::cout << "-----\n";
int main()
    std::cout << std::boolalpha;
    // some implementation-defined facts
    // usually true if 'int' is 32 bit
    std::cout << std::is_same<int, std::int32_t>::value << ' '; // ~ true
    // possibly true if ILP64 data model is used
    std::cout << std::is_same<int, std::int64_t>::value << ' '; // ~ false
    // same tests as above, except using C++17's `std::is_same_v<T, U>` format
    std::cout << std::is_same_v<int, std::int32_t> << ' ';  // ~ true
    std::cout << std::is_same_v<int, std::int64_t> << '\n'; // ~ false
    // compare the types of a couple variables
    long double num1 = 1.0;
    long double num2 = 2.0;
    std::cout << std::is_same_v<decltype(num1), decltype(num2)> << '\n'; // true
    // 'float' is never an integral type
    std::cout << std::is_same<float, std::int32_t>::value << '\n'; // false
    // 'int' is implicitly 'signed'
    std::cout << std::is_same<int, int>::value << ' ';          // true
    std::cout << std::is_same<int, unsigned int>::value << ' '; // false
    std::cout << std::is_same<int, signed int>::value << '\n';  // true
    // unlike other types, 'char' is neither 'unsigned' nor 'signed'
    std::cout << std::is_same<char, char>::value << ' ';          // true
    std::cout << std::is_same<char, unsigned char>::value << ' '; // false
    std::cout << std::is_same<char, signed char>::value << '\n';  // false
    // const-qualified type T is not same as non-const T
    static_assert( not std::is_same<const int, int>() );

Possible output:

true false true false
true false true
true false false

See also

specifies that a type is the same as another type
decltype specifier(C++11) obtains the type of an expression or an entity

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