两种不同类型的集合的set_intersection [英] set_intersection for two different types of sets

问题描述

有两种方法可以对两种不同类型的集合进行std :: set_intersection吗?

Is there any way to do std::set_intersection on two different types of sets?

我有两套:

std::set<X1> l_set1;
std::set<X2> l_set2;

我能够为他们定义一些比较器，以检查X1和X2是否相等.

I'm able to define some comparator for them that checks if X1 and X2 are equal.

struct sample_comparer
{
    bool operator()(const &X1 p_left, const &X2 p_right)
    {
        return p_left == p_right;
    }
};

现在，我尝试在这两个集合上做一个集合交集:

Now, I try to do a set intersection on those two sets:

std::set<X1> l_intersect;
std::set_intersection(l_set1.begin(), l_set1.end(), l_set2.begin(), l_set2.end(),
                      std::inserter(l_intersect, l_intersect.begin()), sample_comparer());

不幸的是，我不能强迫此代码正常工作.我什至不确定这是否可行，但从set_intersection I的描述知道我可以使用两个不同的迭代器.

Unfortunately, I can't force this code to work. I'm not even sure if this is possible, but from the description of set_intersection I know that I can use two different iterators.

我试图搜索一些符合我要求的代码示例，但没有找到?有人可以为我解决我的问题的工作代码示例吗?

I tried to search for some code samples that do what I want, but didn't found any? Could someone present me a working code sample for my problem?

更新: 错误是:

错误:stl_function.h:227:"operator<"不匹配在'__x<中__y'

error: stl_function.h:227: no match for 'operator<' in '__x < __y'

提前谢谢！

推荐答案

PlasmaHH的评论可能是问题所在.

The comment by PlasmaHH is likely the problem.

set_intersection之类的功能的工作方式是:首先执行a < b，然后执行b < a

The way functions like set_intersection work is they first do: a < b and then b < a

因此，ample_comparer需要能够比较两种方式:

As a result ample_comparer needs to be able to compare both ways:

struct sample_comparer
{
    bool operator()(const &X1 p_left, const &X2 p_right)
    {
        return p_left == p_right;
    }
    bool operator()(const &X2 p_left, const &X1 p_right)
    {
        return p_left == p_right;
    }
};

以下内容实际上并没有做任何明智的事情-但它确实可以干净地编译:

The following doesn't actually do anything sensible - but it does compile cleanly:

struct A
{
  struct Compare { bool operator () (A const &, A const &) { return false;}  };
};

struct B
{
  struct Compare { bool operator () (B const &, B const &) { return false; } };
};

typedef std::set<A, A::Compare> S1;
typedef std::set<B, B::Compare> S2;

class IntersectionCompare
{
public:
  bool operator ()(S1::value_type, S2::value_type) { return false; } 
  bool operator ()(S2::value_type, S1::value_type) { return false; } 
};

void bar (S1 & s1, S2 & s2)
{
  S1 result;
  std::set_intersection (s1.begin ()
      , s1.end ()
      , s2.begin ()
      , s2.end ()
      , std :: insert_iterator< S1 > (result, result.end ())
      , IntersectionCompare ());
}

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