# std::is_same

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< cpp‎ | types

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

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

## Inherited from std::integral_constant

### Member constants

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

### Member functions

operator bool | converts the object to bool, returns `value` (public member function)
operator() (C++14) | 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

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

### See also

is_integral (C++11) | checks if a type is an integral type (class template)
make_signed (C++11) | makes the given integral type signed (class template)
make_unsigned (C++11) | makes the given integral type unsigned (class template)

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