c++ - remove_if() 编译错误

Question

VS2010编译错误:

c:\program files (x86)\microsoft visual studio 10.0\vc\include\algorithm(1840): error C2678: binary '=' : no operator found which takes a left-hand operand of type 'const triangle' (or there is no acceptable conversion)h:\kingston_backup\ocv\ocv\delaunay.h(281): could be 'triangle &triangle::operator =(const triangle &)'while trying to match the argument list '(const triangle, const triangle)'c:\program files (x86)\microsoft visual studio 10.0\vc\include\algorithm(1853) : see reference to function template instantiation '_FwdIt std::_Remove_if,_Pr>(_FwdIt,_FwdIt,_Pr)' being compiledwith[  _FwdIt=std::_Tree_unchecked_const_iterator,std::allocator,true>>>,  _Mytree=std::_Tree_val,std::allocator,true>>,  _Pr=triangleIsCompleted]h:\kingston_backup\ocv\ocv\delaunay.cpp(272) : see reference to function template instantiation '_FwdIt std::remove_if,triangleIsCompleted>(_FwdIt,_FwdIt,_Pr)' being compiledwith[  _FwdIt=std::_Tree_const_iterator,std::allocator,true>>>,  _Mytree=std::_Tree_val,std::allocator,true>>,  _Pr=triangleIsCompleted]

I think the problem is in passing the arguments to the remove_if() of the STL, as suggested by the compiler error. I have added the following comment to the line:

//**** ERROR LINE

---

class triangleIsCompleted
{
public:
    triangleIsCompleted(cvIterator itVertex, triangleSet& output, const vertex SuperTriangle[3])
        : m_itVertex(itVertex)
        , m_Output(output)
        , m_pSuperTriangle(SuperTriangle)
    {}

    bool operator()(const triangle& tri) const
    {
        bool b = tri.IsLeftOf(m_itVertex);

        if (b)
        {
            triangleHasVertex thv(m_pSuperTriangle);
            if (! thv(tri)) m_Output.insert(tri);
        }
        return b;
    }
};

// ...

triangleSet workset;
workset.insert(triangle(vSuper));

for (itVertex = vertices.begin(); itVertex != vertices.end(); itVertex++)
{
    tIterator itEnd = remove_if(workset.begin(), workset.end(), triangleIsCompleted(itVertex, output, vSuper)); //**** ERROR LINE
    // ...
}

Answer 1

remove_if 不会删除任何内容(在删除的意义上)。它复制周围的值，以便所有剩余值都在范围的开头结束(并且范围的其余部分或多或少处于未指定的状态)。

由于关联容器中的键是不可变的，因此不可能将值从一个位置复制到另一个位置，因此 remove_if 不能用于它。

标准库似乎不包含 set 的 remove_if，因此您必须自己动手。它可能看起来像这样:

#include <set>

template <class Key, class Compare, class Alloc, class Func>
void erase_if(std::set<Key, Compare, Alloc>& set, Func f)
{
    for (typename std::set<Key, Compare, Alloc>::iterator it = set.begin(); it != set.end(); ) {
        if (f(*it)) {
            set.erase(it++); //increment before passing to erase, because after the call it would be invalidated
        }
        else {
            ++it;
        }
    }
}