CODEWITHSUNDEEP
c++
ZK_
ZK_

Reputation: 564

Why can't operator!= do the conversion?

I have following code with error:

(Visual Studio error:)Error 5 error C2678: binary '!=' : no operator found which takes a left-hand operand of type '` Node' (or there is no acceptable conversion) 

  template <class C, class T>
    C find2 ( C first , C last, T c )
    {
        //
        while ( first != last && *first != c )
        {
            ++first;
        }

        return first;
    }

    struct Node
    {
        Node(int a ,Node* b):val(a),next(b){};
        int val;
        Node* next;
    };

    template <class T>
    struct node_wrap
    {
        T* ptr;

        node_wrap ( T* p = 0 ) : ptr ( p ) {}
        Node& operator*() const {return *ptr;}
        Node* operator->() const {return ptr;}
        node_wrap& operator++ () {ptr = ptr->next; return * this;}
        node_wrap operator++ ( int ) {node_wrap tmp = *this; ++*this; return tmp;}

        bool operator== ( const node_wrap& i ) const {return ptr == i.ptr;}
        bool operator!= ( const node_wrap& i ) const {return ptr != i.ptr;}

    };
    bool operator== ( const Node& node, int n )
    {
        return node.val == n;
    }


    int main()
    {

        Node* node1=new Node(3,NULL);
        Node* node2=new Node(4,NULL);
        node1->next = node2;
        find2 ( node_wrap<Node>(node1), node_wrap<Node>(), 3) ) ;
        delete node1;
        delete node2;
        return 0;
    }

what's wrong with this code?

Upvotes: 0

Views: 176

Answers (2)

Thomas
Thomas

Reputation: 181735

Iterator is of type node_wrap<Node>, so *first returns a Node here:

    while ( first != last && *first != c )

which has no != operator that compares it to the type of c, which is int. You probably meant:

    while ( first != last && first->val != c )

I'd recommend this over the other approach of defining operator== and operator!= that compare Node to int, because these are fundamentally different types and should not be comparable to one another.

Upvotes: 3

interjay
interjay

Reputation: 110088

You are attempting to compare a Node with an int (this is done in the function find2 when performing *first != c).

While you have provided an operator== for comparing a Node with an int, you haven't provided an operator!= to do the same. If you add one, this should work.

Upvotes: 2

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