c - 异常访问 C

Question

我正在制作一个简单的 BST，在 add_to_bst() 函数中，在引用对象的值时，它在第一行抛出错误。

代码

 typedef struct node {
    int value;
    struct node* leftChild;
    struct node* rightChild;
} BSTNode;

BSTNode *new_BSTNode(int val) {
    BSTNode *this = (BSTNode *) malloc(sizeof(BSTNode));
    this->value = val;
    this->leftChild = (BSTNode * ) malloc(sizeof(BSTNode));
    this->rightChild = (BSTNode * ) malloc(sizeof(BSTNode));
    this->leftChild = NULL;
    this->rightChild = NULL;
    return this;
}

typedef struct bst {
    BSTNode * root;
} BST;

BST *new_BST(int root_val) {
    BST *this = (BST *) malloc(sizeof(BST));
    this->root = (BST * ) malloc(sizeof(BSTNode));
    this->root->value = root_val;
//    this->root->value = (int *) malloc(sizeof(int));
    return this;
}


int node_get(BSTNode *n, int i) {
    if (n == NULL) return -1;
    if (i == n-> value) return 1;
    if (i > n-> value) return node_get(n->rightChild, i);
    else return node_get(n->leftChild, i);
}

int bst_get(BST *bst, int i) {
    return node_get(bst->root, i);
}

void add_to_bst_node(int i, BSTNode *to) {
    int n = to->value;                      // <--- ERR
    printf("\nBST VAL: %d", n);

    if (i > n) {
        if (to->rightChild == NULL)
            to->rightChild = new_BSTNode(i);
        else
            add_to_bst_node(i, to->rightChild);
    } else {
        if (to->leftChild == NULL)
            to->leftChild = new_BSTNode(i);
        else
            add_to_bst_node(i, to->leftChild);
    }


}


void add_to_bst(BST *tree, int i) {

    if (tree->root != NULL) {
        add_to_bst_node(i, tree->root);
    } else {
        tree->root = new_BSTNode(i);
    }
}


int main() {

    BST *bst = new_BST(10);
    add_to_bst(bst, 10);

}

运行消息:

0x7fa64fc00690
0x7fa64fc00640
First Val: 10

Process finished with exit code 11

构建错误:

Answer 1

BSTNode *new_BSTNode(int val) {
    BSTNode *this = (BSTNode *) malloc(sizeof(BSTNode));
    this -> value = val;
    this -> leftChild = (BSTNode * ) malloc(sizeof(BSTNode));
    this -> leftChild = (BSTNode * ) malloc(sizeof(BSTNode));
    return this;
}

剩下this->rightChild未初始化并离开 this->leftChild指向未初始化的垃圾。这些问题都没有在调用 new_BSTnode 的代码中得到解决。 .

void add_to_bst_node(int i, BSTNode *to) {
    int n = to -> value;             // <------ ERROR

这并不奇怪，因为 to来自leftChild和rightChild ，这两者都被 new_BSTNode 的逻辑所打破。 .

另外:

BST *new_BST(int root_val) {
    BST *this = (BST *) malloc(sizeof(BST));
    this -> root = (BST * ) malloc(sizeof(BSTNode));
    this -> root -> value = root_val;
//    this -> root -> value = (int *) malloc(sizeof(int));
    return this;
}

这不会设置 this->root->leftChild或this->root->rightChild要么，再说一遍，它们都是垃圾，会被传递到 add_to_bst_node如to .