C ++：不完全类型 [英] C++: incomplete type

问题描述

我有以下代码：

template<class T>
class RandomTreeNode {

public:
    typedef typename RandomTreeFunction<T>::function_ptr function_ptr;
    RandomTreeNode(): left(NULL), right(NULL), threshold(0.0), is_a_leaf(false), data(NULL), function(0){
    }
    void set_function(function_ptr function){this->function = function;}
    function_ptr get_function(){ return this->function;}

    void set_threshold(double threshold){this->threshold = threshold;}
    double get_threshold(){return threshold;}

    void create_left_child(){this->left = RandomTreeNode<T>();}
    //returning references so that they can be altered in a recursive tree build algo without excessive copying
    RandomTreeNode<T>& get_left_child(){return left;}

    void create_right_child(){this->right = RandomTreeNode<T>();}
    RandomTreeNode<T>& get_right_child(){return this->right;}

    bool is_leaf(){return this->is_a_leaf;}
    void mark_as_leaf(){this->is_a_leaf = true;}

    const std::vector<T> get_data(){
        return data;
    }
    void set_data(std::vector<T>& data){
        this->data = data; 
    }

private:
    RandomTreeNode<T> left;
    RandomTreeNode<T> right;
    double threshold;
    function_ptr function;
    std::vector<T> data;
    bool is_a_leaf;

};

当编译时，我得到以下错误：RandomTreeNode< T& :: left'有不完整的类型。任何想法为什么？

推荐答案

因为它是你当前定义的类型。对于类型具有相同类型的成员（对于初学者，它将具有无限大小）没有意义。我想你想要的是具有指向 RandomTreeNode< T> 的指针，而不是直接实例。

Because it's the type you're currently defining. It doesn't make sense for a type to have a member of the same type (for starters, it would have an infinite size). I think what you want is to have pointers to RandomTreeNode<T>'s, not direct instances.

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