在类定义中初始化结构数组

Question

I have a struct that creates nodes for a BST like this

struct BSTNode{
    int data;
    BSTNode *left;
    BSTNode *right;
};

and I need to create an array of these root nodes inside of a class

class HashBST{
public:
    bool lookup(int);
    void insert(int);
    bool remove(int);
    float getLoad();
//private:
    int hash(int);

    BSTNode *table[1019];
    float load;
    int occupied = 0;
    int tableSize = 1019;
};

from there I want to be able to check and see if a BST node has an entry or not. Initially I tried setting the data int to -1 in the struct definition, but in my array in the class, each node had a garbage data value.

Is there a way to set all of the data values to -1, or more ideally, set all the pointers in the table array to NULL until something is stored in them?

Answer 1

Is there a way to set all of the data values to -1,

There isn't because the design of your node implies a specific design of the hash table. Since you have nodes, that implies that you use separate chaining for hash table collision resolution.

And that means your bucket array table needs to be initialized with null pointers, otherwise it contains indeterminate values:

BSTNode* table[1019] = {}; // Zero-initialize buckets.

And then lookup member function is going to look like:

bool HashBST::lookup(int value) {
    unsigned value_hash = hash(value); // Hash must be an unsigned value.
    unsigned index = value_hash % tableSize;
    for(BSTNode* node = table[index]; node; node = node->right) {
        if(node->data == value)
            return true;
    }
    return false;
}

---

In a more advanced version the bucket table should be just a pointer BSTNode* table; which gets initialized with the result of new[] and the size of the referred table is in tableSize .

Answer 2

Here is how I would do it in a C++ friendly way:

Firstly, convert table to std::vector :

std::vector<BSTNode*> table

Create a constructor for HashBst that initializes your std::vector<T*> with all nullptr values.

HashBST() : table(1019) {} //table items are all nullptr