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std::is_same - cppreference.com

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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.

If the program adds specializations for std::is_same or std::is_same_v(since C++17), the behavior is undefined.

Helper variable template

template< class T, class U > 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

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 {};

Example

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

#define SHOW(...) std::cout << #__VA_ARGS__ << " : " << __VA_ARGS__ << '\n'

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

    // some implementation-defined facts

    // usually true if 'int' is 32 bit
    SHOW( std::is_same<int, std::int32_t>::value ); // maybe true
    // possibly true if ILP64 data model is used
    SHOW( std::is_same<int, std::int64_t>::value ); // maybe false

    // same tests as above, except using C++17's std::is_same_v<T, U> format
    SHOW( std::is_same_v<int, std::int32_t> ); // maybe true
    SHOW( std::is_same_v<int, std::int64_t> ); // maybe false

    // compare the types of a couple variables
    long double num1 = 1.0;
    long double num2 = 2.0;
    static_assert( std::is_same_v<decltype(num1), decltype(num2)> == true );

    // 'float' is never an integral type
    static_assert( std::is_same<float, std::int32_t>::value == false );

    // 'int' is implicitly 'signed'
    static_assert( std::is_same_v<int, int> == true );
    static_assert( std::is_same_v<int, unsigned int> == false );
    static_assert( std::is_same_v<int, signed int> == true );

    // unlike other types, 'char' is neither 'unsigned' nor 'signed'
    static_assert( std::is_same_v<char, char> == true );
    static_assert( std::is_same_v<char, unsigned char> == false );
    static_assert( std::is_same_v<char, signed char> == false );

    // const-qualified type T is not same as non-const T
    static_assert( !std::is_same<const int, int>() );
}
#undef SHOW

Possible output: 

std::is_same<int, std::int32_t>::value : true
std::is_same<int, std::int64_t>::value : false
std::is_same_v<int, std::int32_t> : true
std::is_same_v<int, std::int64_t> : false

See also