std::is_signed

STD：：是[医]签名

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

如果T是算术类型，提供成员常量。value平等true如果T(-1) < T(0)*这导致true对于浮点类型和有符号整数类型，false对于无符号整数类型和类型bool...

对于任何其他类型，value是false...

模板参数

T	-	a type to check

辅助变量模板

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

继承自STD：积分[医]常量

成员常数

value static	true if T is a signed arithmetic type , false otherwise (public static member constant)

成员函数

operator bool	converts the object to bool, returns value (public member function)
operator() (C++14)	returns value (public member function)

成员类型

Type	Definition
value_type	bool
type	std::integral_constant<bool, value>

可能的实施

名称空间详细信息{Template<type Name T，bool=std：：is[医]算术<T>*值>结构是[医]签名：STD：：整数[医]常数<bool，T%28-1%29<T%280%29>{}；模板<typename T>结构是[医]签名<T，false>：std：：false[医]类型{}；}//名称空间详细模板<typename T>结构是[医]签名：详细信息：：IS[医]签名<T>*{}型；

*。

例

二次

#include <iostream>
#include <type_traits>
 
class A {};
enum B : int {};
enum class C : int {};
 
int main() 
{
    std::cout << std::boolalpha;
    std::cout << std::is_signed<A>::value << '\n';
    std::cout << std::is_signed<float>::value << '\n';
    std::cout << std::is_signed<signed int>::value << '\n';
    std::cout << std::is_signed<unsigned int>::value << '\n';
    std::cout << std::is_signed<B>::value << '\n';
    std::cout << std::is_signed<C>::value << '\n';
 
    // shorter:
    std::cout << std::is_signed<signed int>() << '\n';
    std::cout << std::is_signed<unsigned int>() << '\n';
}

二次

产出：

二次

false
true
true
false
false
false
true
false

二次

另见

is_unsigned (C++11)	checks if a type is unsigned arithmetic type (class template)
is_signed static	identifies signed types (public static member constant of std::numeric_limits)
is_arithmetic (C++11)	checks if a type is 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)

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