Question

我在下面有两个结构描述。设置huffmanTree = tempNode后，huffmanTree的左右内部指针为NULL。但是，在此之前，该值仍然有效，但在设置两个结构彼此相等之后，该值消失了。我做错了什么？

我只是想创建一个huffmanTree struct并用一些数据初始化它。然后创建一个tempNode，HuffmanTree *left指向huffmanTree，HuffmanTree *right指向新数据。当我从huffmanTree打印出数据时，它是NULL

// Leaf node
typedef struct HuffmanLeaf {
private:
    char data;
    int count;
public:
    HuffmanLeaf() {

    }

    void setData(char data) {
        this->data = data;
    }

    void setCount(int count) {
        this->count = count;
    }

    char getData() {
        return this->data;
    }

    int getCount() {
        return this->count;
    }
}HuffmanLeaf;


// Huffman tree
typedef struct HuffmanTree {
    HuffmanTree *right;
    HuffmanTree *left;
    HuffmanLeaf huffmanLeaf;
} HuffmanTree;

int main() {
     /* huffmanLeaf[] was defined and initialized 
     .
     .
     .
     . 
     */

    // Take the first two smallest and so on
    HuffmanTree huffmanTree;
    HuffmanTree tempNode;

    // Allocate memory for internal struct
    huffmanTree.left = new (HuffmanTree);
    huffmanTree.right = new (HuffmanTree);
    tempNode.left = new (HuffmanTree);
    tempNode.right = new (HuffmanTree);

    // Two character with least frequency. Create a new Tree
    huffmanTree.right->huffmanLeaf = huffmanLeaf[0];
    huffmanTree.left->huffmanLeaf = huffmanLeaf[1];


    // Next character
    tempNode.left = &huffmanTree;   // have node left point to huffmanTree
    tempNode.right->huffmanLeaf = huffmanLeaf[2]; // new data on node right

    /* Data is still here for tempNode */
    cout << tempNode.left->left->huffmanLeaf.getData() << endl;

    /* Error occured after this */
    huffmanTree = tempNode;

    // Value is NULL
    cout << huffmanTree.left->left->huffmanLeaf.getData() << endl; // Value is NULL
}

Answer 1

您执行tempNode.left = &huffmanTree;，之后huffmanTree = tempNode;。如果某事没有出错......那将是一个奇迹......

严肃地说，在转让之前：

huffmanTree is { new, new }
tempNode is { &huffmanTree, new }

分配后，huffmanTree is { &huffmanTree, new }

所以你的指针跳跃本质上是：

huffmanTree->huffmanTree->huffmanTree->huffmanLeaf.GetData();

由于你没有为＆＃34; huffmanTree＆＃34;定义任何huffmanLeaf，它会返回默认情况下的任何值（未定义的行为，因为你没有初始化data in你应该的构造函数）

设置两个相等的结构后，指针为NULL

1 个答案: