比较两组std :: weak_ptr [英] Comparing two sets of std::weak_ptr

问题描述

我想使用GCC 4.7.2比较两组C ++ 11 weak_ptr 。下面的代码显示了再现错误的最小可能示例：

  std :: set< std :: weak_ptr< int> std :: owner_less< std :: weak_ptr< int> > > set1; 
 std :: set< std :: weak_ptr< int>，std :: owner_less< std :: weak_ptr< int> > > set2; 
 
 bool result =（set1 == set2）; 
  

尝试在上面的结果中编译一长串错误，其中以下是第一个实际错误：

  / usr / include / c ++ / 4.7 / bits / stl_algobase.h：791：6：错误： 'operator =='in'__first1.std :: _ Rb_tree_const_iterator< _Tp> :: operator *< std :: weak_ptr< int> >（）== __first2.std :: _ Rb_tree_const_iterator< _Tp> :: operator *< std :: weak_ptr< int> >（）'
  

由于 weak_ptr

一个建议是使用：

  bool result =！（set1< set2）|| < set1））
  

这会导致：

  / usr / include / c ++ / 4.7 / bits / stl_algobase.h：882：6：错误：没有匹配'operator'<'in __first1.std :: _ Rb_tree_const_iterator< _Tp> ; :: operator *< std :: weak_ptr< int> >（） __first2.std :: _ Rb_tree_const_iterator< _Tp> :: operator *< std :: weak_ptr< int> >（）'
  

解决方案

由于weak_ptr不支持'=='，但是在这种情况下你可以使用set的比较运算符try：

  bool result =！ :: lexicographical_compare（set1.begin（），set1.end（），
 set2.begin（），set2.end（），
 set1.value_comp（））|| 
 std： ：lexicographical_compare（set2.begin（），set2.end（），
 set1.begin（），set1.end（），
 set1.value_comp（）））; 
  

这将测试等价性，它缺乏一定的清晰度。

I am trying to compare two sets of C++11 weak_ptr using GCC 4.7.2. The code below shows the smallest possible sample reproducing the error:

std::set<std::weak_ptr<int>, std::owner_less<std::weak_ptr<int> > > set1;
std::set<std::weak_ptr<int>, std::owner_less<std::weak_ptr<int> > > set2;

bool result = (set1 == set2);

Trying to compile the above results in a long list of errors, of which the following is the first actual error:

/usr/include/c++/4.7/bits/stl_algobase.h:791:6: error: no match for ‘operator==’ in ‘__first1.std::_Rb_tree_const_iterator<_Tp>::operator*<std::weak_ptr<int> >() == __first2.std::_Rb_tree_const_iterator<_Tp>::operator*<std::weak_ptr<int> >()’

Due to the transient nature of weak_ptr, is comparing an entire set of them just not possible?

Update:

One suggestion is to use:

bool result = !((set1 < set2) || (set2 < set1))

This results in:

/usr/include/c++/4.7/bits/stl_algobase.h:882:6: error: no match for ‘operator<’ in ‘__first1.std::_Rb_tree_const_iterator<_Tp>::operator*<std::weak_ptr<int> >() < __first2.std::_Rb_tree_const_iterator<_Tp>::operator*<std::weak_ptr<int> >()’

解决方案

Since weak_ptr doesn't support '==', but in this case you can use the comparison operator of the set try:

bool result = !(std::lexicographical_compare(set1.begin(), set1.end(),
                                         set2.begin(), set2.end(),
                                         set1.value_comp()) ||
                std::lexicographical_compare(set2.begin(), set2.end(),
                                         set1.begin(), set1.end(),
                                         set1.value_comp()));

This will test for equivalence, not equality. And it lacks a certain... clarity.

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