写一段二叉树的层序遍历代码，用C++语言

以下是C语言的二叉树层序遍历代码：

#include<stdio.h>
#include<stdlib.h>

struct TreeNode {
    int val;
    struct TreeNode *left;
    struct TreeNode *right;
};

struct QueueNode {
    struct TreeNode* node;
    struct QueueNode* next;
};

struct Queue {
    struct QueueNode* front, * rear;
};

struct QueueNode* createQueueNode(struct TreeNode* node) {
    struct QueueNode* temp = (struct QueueNode*)malloc(sizeof(struct QueueNode));
    temp->node = node;
    temp->next = NULL;
    return temp;
}

struct Queue* createQueue() {
    struct Queue* q = (struct Queue*)malloc(sizeof(struct Queue));
    q->front = q->rear = NULL;
    return q;
}

void enQueue(struct Queue* q, struct TreeNode* node) {
    struct QueueNode* temp = createQueueNode(node);
    if (q->rear == NULL) {
        q->front = q->rear = temp;
        return;
    }
    q->rear->next = temp;
    q->rear = temp;
}

struct TreeNode* deQueue(struct Queue* q) {
    if (q->front == NULL) {
        return NULL;
    }
    struct TreeNode* temp = q->front->node;
    struct QueueNode* tempNode = q->front;
    q->front = q->front->next;
    if (q->front == NULL) {
        q->rear = NULL;
    }
    free(tempNode);
    return temp;
}

int maxDepth(struct TreeNode* root) {
    if (root == NULL) {
        return 0;
    }
    int leftDepth = maxDepth(root->left);
    int rightDepth = maxDepth(root->right);
    return leftDepth > rightDepth ? leftDepth + 1 : rightDepth + 1;
}

void printGivenLevel(struct TreeNode* root, int level) {
    if (root == NULL) {
        return;
    }
    if (level == 1) {
        printf("%d ", root->val);
    }
    else if (level > 1) {
        printGivenLevel(root->left, level - 1);
        printGivenLevel(root->right, level - 1);
    }
}

void levelOrder(struct TreeNode* root) {
    int depth = maxDepth(root);
    for (int i = 1; i <= depth; i++) {
        printGivenLevel(root, i);
    }
}

int main() {
    struct TreeNode* root = (struct TreeNode*)malloc(sizeof(struct TreeNode));
    root->val = 1;
    root->left = (struct TreeNode*)malloc(sizeof(struct TreeNode));
    root->right = (struct TreeNode*)malloc(sizeof(struct TreeNode));
    root->left->val = 2;
    root->right->val = 3;
    root->left->left = (struct TreeNode*)malloc(sizeof(struct TreeNode));
    root->left->right = (struct TreeNode*)malloc(sizeof(struct TreeNode));
    root->left->left->val = 4;
    root->left->right->val = 5;
    root->left->left->left = NULL;
    root->left->left->right = NULL;
    root->left->right->left = NULL;
    root->left->right->right = NULL;
    root->right->left = (struct TreeNode*)malloc(sizeof(struct TreeNode));
    root->right->right = (struct TreeNode*)malloc(sizeof(struct TreeNode));
    root->right->left->val = 6;
    root->right->right->val = 7;
    root->right->left->left = NULL;
    root->right->left->right = NULL;
    root->right->right->left = NULL;
    root->right->right->right = NULL;
    printf("Level order traversal of binary tree is:\n");
    levelOrder(root);
    return 0;
}

这段代码实现了一个基本的二叉树层序遍历算法，使用了队列来辅助实现。在main函数中，我们手动构建了一个二叉树，并输出了层序遍历的结果。