用c语言尽量详细地用括号表示法以非递归的方式输出二叉树的代码

好的，下面是用C语言以非递归的方式输出二叉树的代码，使用了括号表示法：

#include <stdio.h>
#include <stdlib.h>
#include "stack.h" // 自定义栈的头文件

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

// 非递归后序遍历二叉树
void postorder(struct TreeNode* root) {
    if (root == NULL) return;

    struct TreeNode* prev = NULL;
    struct Stack* stack = createStack(); // 创建一个栈
    push(stack, root); // 把根节点压栈

    while (!isEmpty(stack)) {
        struct TreeNode* curr = peek(stack); // 获取栈顶元素

        // 如果当前节点没有子节点或者已经访问过
        if ((curr->left == NULL && curr->right == NULL) ||
            (prev != NULL && (prev == curr->left || prev == curr->right))) {
            printf("%d", curr->val);
            pop(stack); // 弹出栈顶元素
            prev = curr; // 更新prev节点为当前节点
        } else {
            // 右子节点入栈，保证先搜索左子树
            if (curr->right != NULL) push(stack, curr->right);
            // 左子节点入栈
            if (curr->left != NULL) push(stack, curr->left);
        }
    }

    destroyStack(stack); // 销毁栈
}

int main() {
    // 创建以下二叉树
    //      1
    //    /   \
    //   2     3
    //  / \   / \
    // 4   5 6   7
    struct TreeNode* root = (struct TreeNode*)malloc(sizeof(struct TreeNode));
    struct TreeNode* l1 = (struct TreeNode*)malloc(sizeof(struct TreeNode));
    struct TreeNode* r1 = (struct TreeNode*)malloc(sizeof(struct TreeNode));
    struct TreeNode* l2 = (struct TreeNode*)malloc(sizeof(struct TreeNode));
    struct TreeNode* r2 = (struct TreeNode*)malloc(sizeof(struct TreeNode));
    struct TreeNode* l3 = (struct TreeNode*)malloc(sizeof(struct TreeNode));
    struct TreeNode* r3 = (struct TreeNode*)malloc(sizeof(struct TreeNode));

    root->val = 1;
    root->left = l1;
    root->right = r1;

    l1->val = 2;
    l1->left = l2;
    l1->right = r2;

    r1->val = 3;
    r1->left = l3;
    r1->right = r3;

    l2->val = 4;
    l2->left = NULL;
    l2->right = NULL;

    r2->val = 5;
    r2->left = NULL;
    r2->right = NULL;

    l3->val = 6;
    l3->left = NULL;
    l3->right = NULL;

    r3->val = 7;
    r3->left = NULL;
    r3->right = NULL;

    postorder(root); // 输出：4 5 2 6 7 3 1

    free(root);
    free(l1);
    free(r1);
    free(l2);
    free(r2);
    free(l3);
    free(r3);

    return 0;
}

以上是输出二叉树的代码，其中 `Stack` 是我自己封装的栈，可替换为标准库中的栈。