std::is_scalar - cppreference.com (original) (raw)

| | | | | --------------------------------------- | | ------------- | | template< class T > struct is_scalar; | | (since C++11) |

std::is_scalar is a UnaryTypeTrait.

If T is a scalar type, provides the member constant value equal true. For any other type, value is false.

If the program adds specializations for std::is_scalar or std::is_scalar_v, the behavior is undefined.

Contents

• 1 Template parameters
• 2 Helper variable template
• 3 Inherited from std::integral_constant
  • 3.1 Member constants
  • 3.2 Member functions
  • 3.3 Member types
  • 3.4 Notes
  • 3.5 Possible implementation
  • 3.6 Example
  • 3.7 See also

[edit] Template parameters

[edit] Helper variable template

| template< class T > constexpr bool is_scalar_v = is_scalar<T>::value; | | (since C++17) | | --------------------------------------------------------------------------- | | ------------- |

Inherited from std::integral_constant

Member constants

| | true if T is a scalar 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

[edit] Notes

Each individual memory location in the C++ memory model, including the hidden memory locations used by language features (e.g. virtual table pointer), has scalar type (or is a sequence of adjacent bit-fields of non-zero length). Sequencing of side-effects in expression evaluation, inter-thread synchronization, and dependency ordering are all defined in terms of individual scalar objects.

[edit] Possible implementation

[edit] Example

#include #include #include #include   template<typename Head, typename... Tail> void are_scalars(Head&& head, Tail&&... tail) { using T = std::decay_t<decltype(head)>;   std::cout << typeid(T).name() << " is " << (std::is_scalar_v ? "" : "not ") << "a scalar\n";   if constexpr (sizeof... (Tail)) { are_scalars(std::forward<decltype(tail)>(tail)...); } }   int main() { struct S { int m; } s; int S::* mp = &S::m; enum class E { e };   are_scalars(42, 3.14, E::e, "str", mp, nullptr, s); }

Possible output:

int is a scalar double is a scalar main::E is a scalar char const* is a scalar int main::S::* is a scalar nullptr is a scalar main::S is not a scalar

[edit] See also

| | checks if a type is an arithmetic type (class template) [edit] | | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | | checks if a type is an enumeration type (class template) [edit] | | | checks if a type is a pointer type (class template) [edit] | | | checks if a type is a pointer to a non-static member function or object (class template) [edit] |