From cppreference.com
template<classT>structis_signed;(since C++11)std::is_signed is a
.
Checks whether T is a signed arithmetic type.
If std::is_arithmetic<T>::value is true, provides the member constant value equal to T(-1)<T(0).
Otherwise, provides the member constant value equal to false.
If the program adds specializations for std::is_signed or std::is_signed_v, the behavior is undefined.
Template parameters
T - a type to check Helper variable template
template<classT>constexprboolis_signed_v=is_signed<T>::value;(since C++17)Inherited from
Member constants
value
[static]
true if T is a signed arithmetic 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_typebooltypestd::integral_constant<bool,value>Possible implementation
namespacedetail{template<typenameT,bool=std::is_arithmetic<T>::value>structis_signed:std::integral_constant<bool,T(-1)<T(0)>{};template<typenameT>structis_signed<T,false>:std::false_type{};}template<typenameT>structis_signed:detail::is_signed<T>::type{};Example
Run this code
#include<iostream>#include<type_traits>classA{};static_assert(std::is_signed_v<A>==false);classB{inti;};static_assert(std::is_signed_v<B>==false);enumC:int{};static_assert(std::is_signed_v<C>==false);enumclassD:int{};static_assert(std::is_signed_v<D>==false);static_assert(std::is_signed<signedint>::value==trueand// C++11std::is_signed<signedint>()==trueand// C++11std::is_signed<signedint>{}==trueand// C++11std::is_signed_v<signedint>==trueand// C++17std::is_signed_v<unsignedint>==falseandstd::is_signed_v<float>==trueandstd::is_signed_v<bool>==falseandstd::is_signed_v<signedchar>==trueandstd::is_signed_v<unsignedchar>==false);intmain(){// signedness of char is implementation-defined:std::cout<<std::boolalpha<<std::is_signed_v<char><<'\n';}Possible output:
true Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
DR Applied to Behavior as published Correct behavior
C++11 value could be true even if T is not an arithmetic type can only be false in this case See also
(C++11)
checks if a type is an unsigned arithmetic type
(class template)
[static]
identifies signed types
(public static member constant of std::numeric_limits<T>)
(C++11)
checks if a type is an arithmetic type
(class template)
(C++11)
obtains the corresponding signed type for the given integral type
(class template)
(C++11)
obtains the corresponding unsigned type for the given integral type
(class template)
(C++26)
checks if reflection represents a signed arithmetic type
(function)