### 结构体定义
```cpp
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
```cpp
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`
```cpp
// 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
```bash
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
```cpp
#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);
}
```