STL较少运算符和“无效运算符”错误 [英] STL less operator and "invalid operator<" error

问题描述

我有一些代码在VS 10.0中编译良好，但在插入几个项目到Orders地图下面，我收到一个无效的运算符< Microsoft调试库中的错误。我的less运算符很简单，只是比较8字节字符串char by char。任何人都知道为什么会收到此错误？

I have some code that compiles fine in VS 10.0 but after inserting a few items into the Orders map below I receive an "invalid operator <" error in Microsoft debug library. My less operator is simple, just compares the 8 byte string char by char. Anyone have any idea why I would receive this error?

感谢，
Mike

Thanks, Mike

typedef struct MY_orderID_t
{
    char orderID[8];
} MY_orderID_t;

struct std::less<MY_orderID_t>
{ 
   bool operator()(const MY_orderID_t& k1, const MY_orderID_t& k2) const
   {
       for( int i=0; i < 8; i++ )
       {
           if( k1.orderID[i] < k2.orderID[i] )
           return( true );
       }
       return( false );
   }
};

std::map< MY_orderID_t, MY_order_t > Orders[5];

推荐答案

我认为这里的问题是，比较两个 MY_orderID_t 的不是 严格的弱订单 ，是C ++ STL所需的排序关系类型。要成为严格的弱订单，您的小于运算符必须具有以下四个属性：

I believe that the problem here is that your method of comparing two MY_orderID_t's is not a strict weak order, the type of ordering relation required by the C++ STL. To be a strict weak order, your less-than operator must have the following four properties:

1. 反射性 x <


2. 反对称：如果x < y，则y <


3. Transitivity ：如果x < y和y < z，则x <
：如果x和y无法比拟，y和z无法比较，那么x和z是无法比较的。 >

1. Irreflexivity: x < x is always false.
2. Antisymmetry: If x < y, then y < x is always false.
3. Transitivity: If x < y and y < z, then x < z is always true.
4. Transitivity of Equivalence: If x and y are incomparable and y and z are incomparable, then x and z are incomparable.

现在，您的订单不符合属性（2）或（3）。

Right now, your ordering doesn't obey properties (2) or (3).

*首先，（2）被以下内容违反：

*First, (2) is violated by the following:

(0, 4) < (2, 2) 
(2, 2) < (0, 4)

*第二，违反了（3），因为

*Second, (3) is violated, because

(0, 1) < (2, 0) < (-1, 1)

// but 

(0, 1) < (-1, 1) // Fail

要解决这个问题， ，而是使用像这样的 词典比较 ：

To fix this, instead of using the comparison you currently have, instead use a lexicographical comparison like this one:

return std::lexicographical_compare(k1.orderID.begin(), k1.orderID.end(),
                                    k2.orderID.begin(), k2.orderID.end());

这种比较是一个严格的弱排序，是所有STL容器默认使用的。切换到此比较服从属性（1） - （4），并应该使一切正常工作。

This comparison is a strict weak ordering and is what's used by all the STL containers by default. Switching to this comparison obeys properties (1) - (4) and should cause everything to work correctly.

希望这有助于！

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