std::is_scalar
From cppreference.com
Defined in header <type_traits> | ||
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 |
[edit]Template parameters
| T | - | a type to check |
[edit]Helper variable template
template<class T > constexprbool is_scalar_v = is_scalar<T>::value; | (since C++17) | |
Inherited from std::integral_constant
Member constants
value [static] | true if T is a scalar 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> |
[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
template<class T>struct is_scalar :std::integral_constant<bool, std::is_arithmetic<T>::value||std::is_enum<T>::value||std::is_pointer<T>::value||std::is_member_pointer<T>::value||std::is_null_pointer<T>::value>{}; |
[edit]Example
Run this code
#include <iostream>#include <type_traits>#include <typeinfo>#include <utility> 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<T>?"":"not ")<<"a scalar\n"; ifconstexpr(sizeof... (Tail)){ are_scalars(std::forward<decltype(tail)>(tail)...);}} int main(){struct S {int m;} s;int S::* mp =&S::m;enumclass 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
(C++11) | checks if a type is an arithmetic type (class template) |
(C++11) | checks if a type is an enumeration type (class template) |
(C++11) | checks if a type is a pointer type (class template) |
(C++11) | checks if a type is a pointer to a non-static member function or object (class template) |
