从类传递基本构造函数？

Question

 void MovieTree::addMovieNode(int ranking, std::string title, int releaseYear, int quantity)
    {

        std::cout<<"Adding root"<<std::endl;
        if(root == NULL)
        {
            std::cout<<"enter root"<<std::endl;
            MovieNode* root = new MovieNode;    
            root->ranking = ranking;
            root->title = title;
            root->year = releaseYear;
            root->quantity = quantity;
            root->leftChild = root->rightChild = NULL;
            std::cout<<"Item added"<<std::endl;
            std::cout<<title<<std::endl;

        }   

        else if(root)
        {
            std::cout<<"skipped root"<<std::endl;
            MovieNode* newNode = new MovieNode;
            newNode->ranking = ranking;
            newNode->title = title;
            newNode->year = releaseYear;
            newNode->quantity = quantity;


            MovieNode* currentNode = root;
            MovieNode* previousNode = currentNode;

            while(currentNode)
            {
                previousNode = currentNode;

                if(currentNode->title.compare(title) > 0)
                {
                    currentNode = currentNode->rightChild;
                }
                else if(currentNode->title.compare(title) < 0)
                {
                    currentNode = currentNode->leftChild;
                }

            }

            if(previousNode->title.compare(title) > 0)
            {
                previousNode->rightChild = newNode;
            }
            else if(previousNode->title.compare(title) <0)
            {
                previousNode->leftChild = newNode;
            }
        }

    }

This is code for a Binary Search Tree. I'm having some issues with my "addMovieNode" function. It's never entering the initial case wherein I initialize the first node of the BST. I suspect in large part that it's due to my misunderstanding of how to pass the first constructor in my 'main.cpp' driver.

#include "MovieTree.hpp"
#include <iostream>

MovieTree::MovieTree()
{
    MovieNode* root = NULL;

}

void MovieTree::printMovieInventory()
{
    printMovieInventory(root);
}
void MovieTree::printMovieInventory(MovieNode* node)
{
    if(node)
    {
        while(node->rightChild && node->leftChild)
        {
            std::cout<<"Movie:"<<node->title<<" "<<node->quantity<<std::endl;
            if(node->rightChild)
            {
                printMovieInventory(node->rightChild);
            }
            if(node->leftChild)
            {
                printMovieInventory(node->leftChild);
            }
        }
    }
    else
    {
        std::cout<<"No movies in list!"<<std::endl;
    }
}

void MovieTree::addMovieNode(int ranking, std::string title, int releaseYear, int quantity)
{

    std::cout<<"Adding root"<<std::endl;
    if(root == NULL)
    {
        std::cout<<"enter root"<<std::endl;
        MovieNode* root = new MovieNode;    
        root->ranking = ranking;
        root->title = title;
        root->year = releaseYear;
        root->quantity = quantity;
        root->leftChild = root->rightChild = NULL;
        std::cout<<"Item added"<<std::endl;
        std::cout<<title<<std::endl;

    }   

    else if(root)
    {
        std::cout<<"skipped root"<<std::endl;
        MovieNode* newNode = new MovieNode;
        newNode->ranking = ranking;
        newNode->title = title;
        newNode->year = releaseYear;
        newNode->quantity = quantity;


        MovieNode* currentNode = root;
        MovieNode* previousNode = currentNode;

        while(currentNode)
        {
            previousNode = currentNode;

            if(currentNode->title.compare(title) > 0)
            {
                currentNode = currentNode->rightChild;
            }
            else if(currentNode->title.compare(title) < 0)
            {
                currentNode = currentNode->leftChild;
            }

        }

        if(previousNode->title.compare(title) > 0)
        {
            previousNode->rightChild = newNode;
        }
        else if(previousNode->title.compare(title) <0)
        {
            previousNode->leftChild = newNode;
        }
    }

}


void MovieTree::findMovie(std::string title)
{
    if(search(title))
    {
        MovieNode* foundMovie = search(title); 
        std::cout<< "Movie Info:"<<std::endl;
        std::cout<< "==========="<<std::endl;
        std::cout<< "Ranking:"  <<foundMovie->ranking<<std::endl;
        std::cout<< "Title:"        <<foundMovie->title<<std::endl;
        std::cout<< "Year:"     <<foundMovie->year<<std::endl;
        std::cout<< "Quantity:" <<foundMovie->quantity<<std::endl;
    }
    else
    {std::cout<<"Movie not found."<<std::endl;}
}

MovieNode* MovieTree::search(std::string title)
{
    if(root)
    {
        MovieNode* temp = root;
        while(temp && temp->rightChild && temp->leftChild)
        {
            if(!temp)
            {
                if(temp->title == title)
                {
                    return temp;
                }
                else if(temp->title.compare(title) > 0)
                {
                    temp = temp->rightChild;
                }
                else if(temp->title.compare(title) < 0)
                {
                    temp = temp->leftChild;
                }
            }

        }
    }
    else
    {
        std::cout<<"Root does not exist! Movie not found!\n";
    }
}

void MovieTree::rentMovie(std::string title)
{
    if(search(title))
    {
        MovieNode* foundMovie = search(title);

        if(foundMovie->quantity > 0)
        {
            foundMovie->quantity--;
            std::cout<<"Movie has been rented."<<std::endl;
            std::cout<<"Movie Info:"<<std::endl;
            std::cout<<"==========="<<std::endl;
            std::cout<<"Ranking:"<<foundMovie->ranking<<std::endl;
            std::cout<<"Title:"<<foundMovie->title<<std::endl;
            std::cout<<"Year:"<<foundMovie->year<<std::endl;
            std::cout<<"Quantity:"<<foundMovie->quantity<<std::endl;
        }
        else if(foundMovie->quantity == 0)
        {
            std::cout<<"Movie out of stock"<<std::endl;
        }
    }
    else if(!search(title))
    {
        std::cout<<"Movie not found."<<std::endl;
    }
}

The reference in the main.cpp is as follows:

 MovieTree movieTree;

 MovieTree();


 movieTree.addMovieNode(12, "The good and bad", 1870, 12);
 cout<<"Added"<<endl;

I get a segmentation fault after the values are passed through the function and it never enters the initial if(root) statement

Answer 1

In the addMovieNode function you're declaring a local variable root :

MovieNode* root = new MovieNode;

This is hiding the variable root that's a member of the class.

The fix is to remove the declaration, so that the class member is modified instead:

root = new MovieNode;

The same thing is happening in your constructor:

MovieTree::MovieTree()
{
    MovieNode* root = NULL;
}

That needs to be changed to simply root = NULL; as well.