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.
template< class T, class U > inline constexpr bool is_same_v = is_same<T, U>::value; | (since C++17) |
| value
[static] | true if T and U is the same type , false otherwise (public static member constant) |
| operator bool | converts the object to bool, returns value (public member function) |
| operator()
(C++14) | returns value (public member function) |
| Type | Definition |
|---|---|
value_type | bool |
type | std::integral_constant<bool, value> |
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
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
|
(C++11) | checks if a type is an integral type (class template) |
|
(C++11) | makes the given integral type signed (class template) |
|
(C++11) | makes the given integral type unsigned (class template) |
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