std::is_signed

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Technical specifications

Symbols index

External libraries

 

Metaprogramming library

Type traits
Type categories is_void (C++11) is_null_pointer (C++14)   is_array (C++11) is_pointer (C++11) is_enum (C++11) is_union (C++11) is_class (C++11) is_function (C++11) is_object (C++11) is_scalar (C++11) is_compound (C++11) is_integral (C++11) is_floating_point (C++11)   is_fundamental (C++11) is_arithmetic (C++11) is_reference (C++11) is_lvalue_reference (C++11) is_rvalue_reference (C++11) is_member_pointer (C++11) is_member_object_pointer (C++11) is_member_function_pointer (C++11) Type properties is_const (C++11) is_volatile (C++11) is_empty (C++11) is_polymorphic (C++11) is_final (C++14) is_abstract (C++11) is_aggregate (C++17) is_implicit_lifetime (C++23) is_trivial (C++11) is_trivially_copyable (C++11) is_standard_layout (C++11) is_literal_type (C++11)(until C++20*) is_pod (C++11)(deprecated in C++20) is_signed (C++11) is_unsigned (C++11) is_bounded_array (C++20) is_unbounded_array (C++20) is_scoped_enum (C++23) has_unique_object_representations (C++17) Type trait constants integral_constantbool_constanttrue_typefalse_type (C++11)(C++17)(C++11)(C++11) Metafunctions conjunction (C++17) disjunction (C++17) negation (C++17)	Supported operations is_constructibleis_trivially_constructibleis_nothrow_constructible (C++11)(C++11)(C++11) is_default_constructibleis_trivially_default_constructibleis_nothrow_default_constructible (C++11)(C++11)(C++11) is_copy_constructibleis_trivially_copy_constructibleis_nothrow_copy_constructible (C++11)(C++11)(C++11) is_move_constructibleis_trivially_move_constructibleis_nothrow_move_constructible (C++11)(C++11)(C++11) is_assignableis_trivially_assignableis_nothrow_assignable (C++11)(C++11)(C++11) is_copy_assignableis_trivially_copy_assignableis_nothrow_copy_assignable (C++11)(C++11)(C++11) is_move_assignableis_trivially_move_assignableis_nothrow_move_assignable (C++11)(C++11)(C++11) is_destructibleis_trivially_destructibleis_nothrow_destructible (C++11)(C++11)(C++11) has_virtual_destructor (C++11) is_swappable_withis_swappableis_nothrow_swappable_withis_nothrow_swappable (C++17)(C++17)(C++17)(C++17) Relationships and property queries is_same (C++11) is_base_of (C++11) is_convertibleis_nothrow_convertible (C++11)(C++20) is_layout_compatible (C++20) is_pointer_interconvertible_base_of (C++20) is_pointer_interconvertible_with_class (C++20)   is_corresponding_member (C++20) alignment_of (C++11) rank (C++11) extent (C++11) is_invocableis_invocable_ris_nothrow_invocableis_nothrow_invocable_r (C++17)(C++17)(C++17)(C++17) reference_constructs_from_temporary (C++23) reference_converts_from_temporary (C++23) Type modifications remove_cvremove_constremove_volatile (C++11)(C++11)(C++11) add_cvadd_constadd_volatile (C++11)(C++11)(C++11) make_signed (C++11) make_unsigned (C++11) remove_reference (C++11) add_lvalue_referenceadd_rvalue_reference (C++11)(C++11) remove_pointer (C++11) add_pointer (C++11) remove_extent (C++11) remove_all_extents (C++11) Type transformations aligned_storage (C++11)(deprecated in C++23) aligned_union (C++11)(deprecated in C++23) decay (C++11) remove_cvref (C++20) enable_if (C++11) void_t (C++17) conditional (C++11) common_type (C++11) common_reference (C++20) underlying_type (C++11) result_ofinvoke_result (C++11)(until C++20*)(C++17) type_identity (C++20)
Compile-time rational arithmetic
Compile-time integer sequences
integer_sequence (C++14)

 

Defined in header <type_traits>
template< class T > struct is_signed;		(since C++11)

std::is_signed is an UnaryTypeTrait.

If T is an arithmetic type, provides the member constant value equal to true if T(-1) < T(0): this results in true for the floating-point types and the signed integer types, and in false for the unsigned integer types and the type bool.

For any other type, value is false.

The behavior of a program that adds specializations for std::is_signed or std::is_signed_v (since C++17) is undefined.

Template parameters

T

-

a type to check

Helper variable template

template< class T > inline constexpr bool is_signed_v = is_signed<T>::value;		(since C++17)

Inherited from std::integral_constant

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_type	bool
type	std::integral_constant<bool, value>

Possible implementation

namespace detail { template<typename T,bool = std::is_arithmetic<T>::value> struct is_signed : std::integral_constant<bool, T(-1) < T(0)> {};   template<typename T> struct is_signed<T,false> : std::false_type {}; } // namespace detail   template<typename T> struct is_signed : detail::is_signed<T>::type {};

Example

Run this code

#include <iostream>
#include <type_traits>
 
class A {};
enum B : int {};
enum class C : int {};
 
int main()
{
    static_assert(std::is_signed<A>::value == false);
    static_assert(std::is_signed<float>::value == true);
    static_assert(std::is_signed<signed int>::value == true);
    static_assert(std::is_signed<unsigned int>::value == false);
    static_assert(std::is_signed<B>::value == false);
    static_assert(std::is_signed<C>::value == false);
 
    // shorter:
    static_assert(std::is_signed_v<bool> == false);
    static_assert(std::is_signed<signed int>() == true);
    static_assert(std::is_signed<unsigned int>{} == false);
    static_assert(std::is_signed_v<signed char> == true);
    static_assert(std::is_signed_v<unsigned char> == false);
 
    // signedness of char is implementation-defined:
    std::cout << std::boolalpha << std::is_signed_v<char> << '\n';
}

Possible output:

true

See also

is_unsigned (C++11)	checks if a type is an unsigned arithmetic type (class template)
is_signed [static]	identifies signed types (public static member constant of std::numeric_limits<T>)
is_arithmetic (C++11)	checks if a type is an arithmetic type (class template)
make_signed (C++11)	makes the given integral type signed (class template)
make_unsigned (C++11)	makes the given integral type unsigned (class template)