输入一棵二叉搜索树，将其转化成一个排序的双向链表，c语言实现

好的，以下是实现代码：

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

// 定义二叉树结构体
struct TreeNode {
    int val;
    struct TreeNode *left;
    struct TreeNode *right;
};

// 定义双向链表结构体
struct ListNode {
    int val;
    struct ListNode *prev;
    struct ListNode *next;
};

// 递归函数，将二叉搜索树转化为排序的双向链表
void convertBSTtoDLL(struct TreeNode* root, struct ListNode **head, struct ListNode **tail) {
    if (root == NULL) {
        return;
    }

    // 对左子树进行转化
    convertBSTtoDLL(root->left, head, tail);

    // 将当前节点添加到双向链表中
    struct ListNode *node = (struct ListNode *)malloc(sizeof(struct ListNode));
    node->val = root->val;
    node->prev = NULL;
    node->next = NULL;

    if (*head == NULL) {
        *head = node;
    } else {
        (*tail)->next = node;
        node->prev = *tail;
    }

    *tail = node;

    // 对右子树进行转化
    convertBSTtoDLL(root->right, head, tail);
}

// 主函数，调用递归函数将二叉树转化为排序的双向链表
struct ListNode* BSTtoDLL(struct TreeNode* root) {
    if (root == NULL) {
        return NULL;
    }

    struct ListNode *head = NULL;
    struct ListNode *tail = NULL;

    convertBSTtoDLL(root, &head, &tail);

    return head;
}

// 测试函数
int main() {
    // 创建一棵二叉搜索树
    struct TreeNode *root = (struct TreeNode *)malloc(sizeof(struct TreeNode));
    root->val = 4;

    struct TreeNode *node1 = (struct TreeNode *)malloc(sizeof(struct TreeNode));
    node1->val = 2;

    struct TreeNode *node2 = (struct TreeNode *)malloc(sizeof(struct TreeNode));
    node2->val = 5;

    struct TreeNode *node3 = (struct TreeNode *)malloc(sizeof(struct TreeNode));
    node3->val = 1;

    struct TreeNode *node4 = (struct TreeNode *)malloc(sizeof(struct TreeNode));
    node4->val = 3;

    root->left = node1;
    root->right = node2;

    node1->left = node3;
    node1->right = node4;

    node2->left = NULL;
    node2->right = NULL;

    node3->left = NULL;
    node3->right = NULL;

    node4->left = NULL;
    node4->right = NULL;

    // 将二叉搜索树转化为排序的双向链表
    struct ListNode *head = BSTtoDLL(root);

    // 输出双向链表中的值
    while (head != NULL) {
        printf("%d ", head->val);
        head = head->next;
    }
    printf("\n");

    return 0;
}

该程序中，convertBSTtoDLL 函数是递归函数，用于将二叉搜索树转化为排序的双向链表；BSTtoDLL 函数是主函数，调用 convertBSTtoDLL 函数将二叉搜索树转化为排序的双向链表；最后，测试函数创建一棵二叉搜索树，将其转化为排序的双向链表，并输出双向链表中的值。