如何访问类中结构的数据成员？

Question

I've wrote this class, and the member function, and have created the object in the main function. It calls the show function just fine, but the show function itself says that it cannot access root because it is not declared in scope. I set the data members as public, and I didn't think I would need a getter/setter for this. What's the best way to allow show() access to root?

class bst
{
            public:
            struct Node
            {
                public:
                int data;
                struct Node *left;
                struct Node *right;
                Node* root = NULL;
            };

            void show();

};

void bst::show()
{
    if(root == NULL) return;

    show(root->left);       //Visit left subtree
    printf("%d ",root->data);  //Print data
    show(root->right);      // Visit right subtree
}

Answer 1

It doesn't look like you actually defined an instance of struct Node as a member of your bst class. You defined the nested class, but declared no instances of it. Declare one, and you can use the name it's declared under to make this work, eg:

class bst
{
            public:
            struct Node
            {
                public:
                int data;
                struct Node *left;
                struct Node *right;
                Node* root = NULL;
            };
            Node node;

            void show();
};


void bst::show()
{
    if(node.root == NULL) return;

    show(node.root->left);       //Visit left subtree
    printf("%d ",node.root->data);  //Print data
    show(node.root->right);      // Visit right subtree
}

It's possible you meant for root to be a member of bst , in which case you'd rearrange things to put it in bst , not the declaration of the Node class:

class bst
{
            public:
            struct Node
            {
                public:
                int data;
                struct Node *left;
                struct Node *right;
            };
            Node* root = NULL;

            void show();
};

in which case you wouldn't need to qualify the references with node. as shown in the first example.