结构体定义

typedef struct BTreeNode {
    // 4，填充对齐到8
    DATA_TYPE data;
    // 8 + 8
    struct BTreeNode *lChild, *rChild;
} BTreeNode, *BTree;
​

初始化代码

BTree createBTree(DATA_TYPE value) {
    BTree bTree = (BTree) malloc(sizeof (BTreeNode));
    bTree->data = value;
    bTree->lChild = nullptr;
    bTree->rChild = nullptr;
    return bTree;
}

void setBTreeChild(BTree &node, BTree left, BTree right) {
    node->lChild = left;
    node->rChild = right;
}

BTree initBTree1() {
    BTree node1 = createBTree(1);
    BTree node2 = createBTree(2);
    BTree node3 = createBTree(3);
    BTree node4 = createBTree(4);
    BTree node5 = createBTree(5);
    BTree node6 = createBTree(6);
    BTree node7 = createBTree(7);
    BTree node8 = createBTree(8);
    BTree node9 = createBTree(9);
    BTree node10 = createBTree(10);
    BTree node11 = createBTree(11);
    BTree node12 = createBTree(12);
    BTree node13 = createBTree(13);
    BTree node14 = createBTree(14);
    BTree node15 = createBTree(15);
    setBTreeChild(node1, node2, node3);
    setBTreeChild(node2, node4, node5);
    setBTreeChild(node3, node6, node7);
    setBTreeChild(node4, node8, node9);
    setBTreeChild(node5, node10, node11);
    setBTreeChild(node6, node12, node13);
    setBTreeChild(node7, node14, node15);
    return node1;
}
​

问题复盘

sizeof 如果也用 BTree 就会出现问题，这问题也太隐蔽了；因为 BTree 其实是一个指向 BTreeNode 结构体的指针类型变量，指针变量长度只有 8 字节，而 BTreeNode 实际至少 4+8+8=20字节 ，经过对齐填充后变为 24字节

// 8
size_t i2 = sizeof(BTree);
// 24
size_t i3 = sizeof(BTreeNode);
// 重点在这行代码，实际size=20，填充后为24
BTree bTree = (BTree) malloc(sizeof (BTreeNode));
​

因此正确申请内存的写法是 malloc(sizeof (结构体原名))，手动改为 BTree bTree = (BTree) malloc(20); 后，程序也可以正常运行

1       2       4       8       9       5       10      11      3       6       12      13      7       14      15      
Process finished with exit code 0
​

其余代码

#include "cstdio"
#include "cstdlib"

using namespace std;
#define DATA_TYPE int

int main() {
    // 初始化二叉树
    BTree b1 = initBTree1();
    preOrder(b1);
    return 0;
}

void visit(BTree pNode);

void preOrder(BTree bTree) {
    if (bTree == nullptr) {
        return;
    }

    visit(bTree);

    preOrder(bTree->lChild);
    preOrder(bTree->rChild);
}

void visit(BTree pNode) {
    if (pNode == nullptr) {
        return;
    }
    printf("%d\t", pNode->data);
}
​