实现红黑树的分段故障

Question

这是关于Stack Overflow的第一个问题！

我必须实现一个红黑树，但由于某种原因，我在运行代码时遇到了分段错误。我已经经历了一千次，但似乎无法弄清楚我哪里出错了。希望其他人可以选择我错过的东西。

程序从文本文件中读取单词并尝试将每个单词插入到RB树中。我编写了一个类似的程序，使用字符串比较运算符插入二叉搜索树，所以我不认为这是问题。

#include <iostream>
#include <string>
#include <fstream>

using namespace std;

enum color {red,black};

struct node{
    enum color color;
    string value;
    node *leftChild,*rightChild,*parent;
};

class RBT{
private:
    string filename;
    node* root = NULL;

    int readfile(){//read file and insert each word into BST
        ifstream file;
        file.open (filename.c_str());
        if (!file.is_open()) return 1;
        string word;
        while (file >> word){// for each word in file
            insert(word);
        }
        return 0;
    }

    void left_rotate(node* x){
        node* y = x->rightChild;
        x->rightChild = y->leftChild;
        if(y->leftChild != NULL)
            y->leftChild->parent = x;
        y->parent = x->parent;
        if(x->parent == NULL)
            root = y;
        else if(x->parent->leftChild == x)
            x->parent->leftChild = y;
        else
            x->parent->rightChild = y;
        y->leftChild = x;
        x->parent = y;
    }

    void right_rotate(node* y){
        node* x = y->leftChild;
        y->leftChild = x->rightChild;
        if(x->rightChild != NULL)
            x->rightChild->parent = y;
        x->parent = y->parent;
        if(y->parent == NULL)
            root = x;
        else if(y->parent->leftChild == y)
            y->parent->leftChild = x;
        else
            y->parent->rightChild = x;
        x->rightChild = y;
        y->parent = x;
    }

    void insert_fix(node* z){
        while (z->parent->color == red) {
            if (z->parent == z->parent->parent->leftChild) {
                node* y = z->parent->parent->rightChild;
                if(y->color == red){
                    z->parent->color = black;
                    y->color = black;
                    z->parent->parent->color = red;
                    z = z->parent->parent;
                }
                else{
                    if(z == z->parent->rightChild){
                        z = z->parent;
                        left_rotate(z);
                    }
                    z->parent->color = black;
                    z->parent->parent->color = red;
                    right_rotate(z->parent->parent);
                }
            }
            else{
                node* y = z->parent->parent->leftChild;
                if(y->color == red){
                    z->parent->color = black;
                    y->color = black;
                    z->parent->parent->color = red;
                    z = z->parent->parent;
                }
                else {
                    if(z == z->parent->leftChild){
                        z = z->parent;
                        right_rotate(z);
                    }
                    z->parent->color = black;
                    z->parent->parent->color = red;
                    left_rotate(z->parent->parent);
                }
            }
        }
        (root)->color = black;
    }

    void tree_insert(node* Z){
        node* y = NULL;
        node* x = root;
        while(x != NULL) {
            y = x;
            if(Z->value < x->value){
                x = x->leftChild;
            }
            else if (Z->value > x->value){
                x = x->rightChild;
            }
            else{
                return;
            }
        }
        Z->parent = y;
        if(y == NULL)
            root = Z;
        else if(Z->value < y->value)
            y->leftChild = Z;
        else
            y->rightChild = Z;
        Z->leftChild = NULL;
        Z->rightChild = NULL;
        Z->color = red;
        insert_fix(Z);
    }
public:
    RBT(string _filename);
    void insert(string S){
        node* strNode = new node;
        strNode->value=S;
        strNode->leftChild=NULL;
        strNode->rightChild=NULL;
        strNode->parent=NULL;
        tree_insert(strNode);
    }
};
RBT::RBT(string _filename){
    filename = _filename;
    root = new node;
    readfile();
    }

int main(){
    RBT rbt1 ("words.txt");
}