is_signed 類別

測試類型是否為帶正負號的整數。

語法

template <class Ty>
struct is_signed;

參數

Ty
要查詢的類型。

備註

如果類型 Ty 是帶正負號整數類型或cv-qualified帶正負號整數型別，則類型述詞的實例會保留 true，否則為 false。

範例

// std__type_traits__is_signed.cpp
// compile with: /EHsc
#include <type_traits>
#include <iostream>

struct trivial
    {
    int val;
    };

int main()
    {
    std::cout << "is_signed<trivial> == " << std::boolalpha
        << std::is_signed<trivial>::value << std::endl;
    std::cout << "is_signed<int> == " << std::boolalpha
        << std::is_signed<int>::value << std::endl;
    std::cout << "is_signed<unsigned int> == " << std::boolalpha
        << std::is_signed<unsigned int>::value << std::endl;
    std::cout << "is_signed<float> == " << std::boolalpha
        << std::is_signed<float>::value << std::endl;

    return (0);
    }

is_signed<trivial> == false
is_signed<int> == true
is_signed<unsigned int> == false
is_signed<float> == true

需求

標頭：<type_traits>

命名空間：std

另請參閱

<type_traits>
is_unsigned 類別