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std::is_same(3) C++ Standard Libary std::is_same(3) 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 (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 > (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 are the same type , false otherwise [static] (public static member constant) Member functions operator bool converts the object to bool, returns value (public member function) operator() returns value (C++14) (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 // 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 print_separator(); // 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 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 << ' '; // true std::cout << std::is_same<int, unsigned int>::value << ' '; // 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 << ' '; // 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 false true ----- true false false See also same_as specifies that a type is the same as an- other type (C++20) (concept) decltype specifier(C++11) obtains the type of an expression or an entity http://cppreference.com 2022.07.31 std::is_same(3)
NAME | Synopsis | Member constants | Member functions | Member types | Possible implementation | Example | Possible output: | See also
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