std::rel_ops::operator!=,>,<=,>=

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C++
 
实用工具库
类型的支持 (basic types, RTTI, type traits)
动态内存管理
错误处理
程序实用工具
可变参数函数
日期和时间
函数对象
initializer_list（C++11）
bitset
hash（C++11）
关系运算符
Original:
Relational operators
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rel_ops::operator!=
rel_ops::operator>
rel_ops::operator<=
rel_ops::operator>=
双和元组
Original:
Pairs and tuples
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pair
tuple（C++11）
piecewise_construct_t（C++11）
piecewise_construct（C++11）
掉期，远期和移动
Original:
Swap, forward and move
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swap
forward（C++11）
move（C++11）
move_if_noexcept（C++11）
declval（C++11）
 
Defined in header <utility>
template< class T >
bool operator!=( const T& lhs, const T& rhs );
 (1)
template< class T >
bool operator>( const T& lhs, const T& rhs );
 (2)
template< class T >
bool operator<=( const T& lhs, const T& rhs );
 (3)
template< class T >
bool operator>=( const T& lhs, const T& rhs );
 (4)
给定的一个用户定义的operator==和operator<类型T的对象，实现其它比较运算符通常的语义.
Original:
Given a user-defined operator== and operator< for objects of type T, implements the usual semantics of other comparison operators.
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1)
实现operator!=的operator==.
Original:
Implements operator!= in terms of operator==.
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2)
实现operator>的operator<.
Original:
Implements operator> in terms of operator<.
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3)
实现operator<=的operator<.
Original:
Implements operator<= in terms of operator<.
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4)
实现operator>=的operator<.
Original:
Implements operator>= in terms of operator<.
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目录

[编辑] 参数

lhs -
左边的参数
Original:
left-hand argument
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rhs -
右手的说法
Original:
right-hand argument
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[编辑] 返回值

1)
返回truelhs是“不等于”rhs.
Original:
Returns true if lhs is not equal to rhs.
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2)
如果true返回lhs是“更大的”比rhs.
Original:
Returns true if lhs is greater than rhs.
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3)
返回truelhs是“小于或等于”rhs.
Original:
Returns true if lhs is less or equal to rhs.
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4)
返回truelhs是“大于或等于”rhs.
Original:
Returns true if lhs is greater or equal to rhs.
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[编辑] 可能的实现

First version 
namespace rel_ops {
    template< class T >
    bool operator!=( const T& lhs, const T& rhs )
    {
        return !(lhs == rhs);
    }
}
Second version 
namespace rel_ops {
    template< class T >
    bool operator>( const T& lhs, const T& rhs )
    {
        return rhs < lhs;
    }
}
Third version 
namespace rel_ops {
    template< class T >
    bool operator<=( const T& lhs, const T& rhs )
    {
        return !(rhs < lhs);;
    }
}
Fourth version 
namespace rel_ops {
    template< class T >
    bool operator>=( const T& lhs, const T& rhs )
    {
        return !(lhs < rhs);
    }
}

[编辑] 为例

#include <iostream>
#include <utility>
 
struct Foo {
    int n;
};
 
bool operator==(const Foo& lhs, const Foo& rhs)
{
    return lhs.n == rhs.n;
}
 
bool operator<(const Foo& lhs, const Foo& rhs)
{
    return lhs.n < rhs.n;
}
 
int main()
{
    Foo f1 = {1};
    Foo f2 = {2};
    using namespace std::rel_ops;
 
    std::cout << std::boolalpha;
    std::cout << "not equal?     : " << (bool) (f1 != f2) << '\n';
    std::cout << "greater?       : " << (bool) (f1 > f2) << '\n';
    std::cout << "less equal?    : " << (bool) (f1 <= f2) << '\n';
    std::cout << "greater equal? : " << (bool) (f1 >= f2) << '\n';
}

Output: 

not equal?     : true
greater?       : false
less equal?    : true
greater equal? : false
来自“http://zh.cppreference.com/mwiki/index.php?title=cpp/utility/rel_ops/operator_cmp&oldid=26402”