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std:: ratio_equal

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ratio_equal
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定义于头文件 <ratio>
template < class R1, class R2 >
struct ratio_equal : std:: integral_constant < bool , /* 见下文 */ > { } ;
(C++11 起)

如果比例 R1 和 R2 相等，则成员常量 value 等于 true 。否则， value 为 false 。

目录

辅助变量模板

template < class R1, class R2 >
constexpr bool ratio_equal_v = ratio_equal < R1, R2 > :: value ;
(C++17 起)

继承自 std:: integral_constant

成员常量

value
[static]
若 R1 :: num == R2 :: num && R1 :: den == R2 :: den 则为 true ，否则为 false
(公开静态成员常量)

成员函数

operator bool
转换对象为 bool ，返回 value
(公开成员函数)
operator()
(C++14)
返回 value
(公开成员函数)

成员类型

类型 定义
value_type bool
type std:: integral_constant < bool , value >

可能的实现 

template< class R1, class R2 >
struct ratio_equal : public std::integral_constant <
                                 bool,
                                 R1::num == R2::num && R1::den == R2::den
                            > {};

示例

运行此代码 
#include <iostream>
#include <ratio>
int main()
{
    constexpr bool equ = std::ratio_equal_v<std::ratio<2,3>,
                                            std::ratio<6,9>>;
    static_assert(equ);
    std::cout << "2/3 " << (equ ? "==" : "!=") << " 6/9\n";
}

输出： 

2/3 == 6/9

参见

(C++11)
在编译时比较两个 ratio 对象是否不相等
(类模板)