Question

我遇到以下课程的问题。我得到错误＆＃34; Tree.cpp：12：56：错误：模板参数列表中参数2的类型/值不匹配'template class std :: multiset'// Tree.cpp：12：56：注意：预期一个类型，得到'（Tree :: compare＆lt;）'＆＃34;。我不明白我应该如何在multiset声明中传递比较器类型。你能帮帮我吗？

#include <set>
#include <deque>
#include <iostream>
using namespace std;

template <typename T>
class Tree
{
    typedef typename std::multiset<Tree<T>*, typename Tree<T>::compare > NodeSet;

private:
    NodeSet children;
    T content;

public:
    struct compare
    {
        bool operator()( const Tree*& t1, const Tree*& t2 ) const
        {
            cout << "Comparing " << t1->GetContent() << " vs " << t2->GetContent() << endl;
            return t1->GetContent() < t2->GetContent();
        }
    };
    Tree& AppendNode( const T& node )
    {
        Tree* t = new Tree( node );
        AttachTree( t );
        return *t;
    }
    void Clear()
    {
        typename NodeSet::iterator it = children.begin();
        while( children.size() != 0 && children.end() != it )
        {

            children.erase( *it );
            delete *it;
            it++;
        }
    }
    Tree( const T& root )
    {
        content = root;
    }
    void AttachTree( Tree* t )
    {
        children.insert( t );
    }
    void Visit( std::deque<T>& exp ) const
    {
        exp.push_back( content );
        typename NodeSet::iterator it = children.begin();
        while( it != children.end() )
        {
            ( *it )->Visit( exp ); it++;
        }
    }
    Tree()
    {}
    Tree( Tree& c )
    {
        c.DeepCopyTo( this );
    }
    T& operator =( const Tree& b )
    {
        b.DeepCopyTo( this );
    }
    ~Tree()
    {
        cout << "in destructor for" << this << endl;
        Clear();
    }
    void DeepCopyTo( Tree* dest ) const
    {
        dest->content = content;
        typename NodeSet::iterator it = children.begin();
        while( it != children.end() )
        {
            Tree* t = new Tree();
            ( *it )->DeepCopyTo( t );
            dest->AttachTree( t );
            it++;
        }
    }
    void Print()
    {
        typename NodeSet::iterator it = children.begin();
        while( it != children.end() )
        {
            cout << *it << ",";
            it++;
        }
    }
};

int main()
{
    Tree<int> tree( 8 );
    tree.AppendNode( 5 );
}

Answer 1

您可能希望将此行更改为

typedef 
    typename std::multiset<Tree*, typename Tree::compare > 
    NodeSet;

请注意，compare是dependent name，因此您需要使用typename。

此外，您应该考虑将结构compare移到此行上方，因为此行引用它。

还有两件事要注意。

您可能希望将compare更改为

struct compare {
    bool operator()(const Tree* t1, const Tree* t2) const {
    cout << "Comparing " <<t1->GetContent() <<" vs "<<t2->GetContent()<<endl;                                                                                        
        return t1->GetContent() < t2->GetContent();
    }   
};

不幸的是，GetContent似乎无法在代码中的任何位置定义。

在类中声明自定义比较器时类型/值不匹配

1 个答案: