c - btree 实现中的段错误

Question

任何人都可以帮助消除此段错误。我已经在这个代码上工作了一个星期仍然无法调试它。这段代码是Btree的实现。插入部分工作正常，但删除部分出现段错误。我无法调试它，有人可以帮忙吗？

我已经根据此链接给出了输入(已将字母值转换为 ASCII 值) http://cis.stvincent.edu/html/tutorials/swd/btree/btree.html

当我删除第一个 H (等效 ASCII 值)时，它可以正常工作，但是当我删除 T (等效 ASCII 值)时，我会遇到段错误。

    #include<stdio.h>
    #include<stdlib.h>
    #define M 5

    struct node{
        int n; /* n < M No. of keys in node will always less than order of B
              tree */
        int keys[M-1]; /*array of keys*/
        struct node *p[M]; /* (n+1 pointers will be in use) */
    }*root=NULL;

    enum KeyStatus { Duplicate,SearchFailure,Success,InsertIt,LessKeys };

    void insert(int key);
    void display(struct node *root,int);
    void DelNode(int x);
    void search(int x);
    enum KeyStatus ins(struct node *r, int x, int* y, struct node** u);
    int searchPos(int x,int *key_arr, int n);
    enum KeyStatus del(struct node *r, int x);
    int input_array[20]= {65,67,71,78,72,69,75,81,77,70,87,76,84,90,68,80,82,88,89,83};
    int main()
    {

        int choice, i,key = 11;
        printf("Creation of B tree for node %d\n",M);
        while(1)
        {
            printf("1.Insert\n");
            printf("2.Delete\n");
            printf("3.Search\n");
            printf("4.Display\n");
            printf("5.Quit\n");
            printf("Enter your choice : ");
            scanf("%d",&choice);

            switch(choice)
            {
                case 1:
                    //printf("Enter the key : ");
                    //scanf("%d",&key);
                    //for(i=0;i<20;i++)
                     for(i=0;i<20;i++)
                     {
                        key = input_array[i];
                        insert(key);
                     }  
                    //insert(key++);
                    //insert(key);
                    break;
                case 2:
                    printf("Enter the key : ");
                    scanf("%d",&key);
                    DelNode(key);
                    break;
                case 3:
                    printf("Enter the key : ");
                    scanf("%d",&key);
                    search(key);
                    break;
                case 4:
                    printf("Btree is :\n");
                    display(root,0);
                    break;
                case 5:
                    exit(1);
                default:
                    printf("Wrong choice\n");
                    break;
            }/*End of switch*/
        }/*End of while*/
        return 0;
    }/*End of main()*/

    void insert(int key)
    {
        struct node *newnode;
        int upKey;
        enum KeyStatus value;
        value = ins(root, key, &upKey, &newnode);
        if (value == Duplicate)
            printf("Key already available\n");
        if (value == InsertIt)
        {
            struct node *uproot = root;
            root=malloc(sizeof(struct node));
            root->n = 1;
            root->keys[0] = upKey;
            root->p[0] = uproot;
            root->p[1] = newnode;
        }/*End of if */
    }/*End of insert()*/

    enum KeyStatus ins(struct node *ptr, int key, int *upKey,struct node **newnode)
    {
        struct node *newPtr, *lastPtr;
        int pos, i, n,splitPos;
        int newKey, lastKey;
        enum KeyStatus value;
        if (ptr == NULL)
        {
            *newnode = NULL;
            *upKey = key;
            return InsertIt;
        }
        n = ptr->n;
        pos = searchPos(key, ptr->keys, n);

        if (pos < n && key == ptr->keys[pos])
            return Duplicate;
        value = ins(ptr->p[pos], key, &newKey, &newPtr);
        if (value != InsertIt)
            return value;
        /*If keys in node is less than M-1 where M is order of B tree*/
        if (n < M - 1)
        {
            pos = searchPos(newKey, ptr->keys, n);
            /*Shifting the key and pointer right for inserting the new key*/
            for (i=n; i>pos; i--)
            {
                ptr->keys[i] = ptr->keys[i-1];
                ptr->p[i+1] = ptr->p[i];
            }
            /*Key is inserted at exact location*/
            ptr->keys[pos] = newKey;
            ptr->p[pos+1] = newPtr;
            ++ptr->n; /*incrementing the number of keys in node*/
            return Success;
        }/*End of if */
        /*If keys in nodes are maximum and position of node to be inserted is
          last*/
        if (pos == M - 1)
        {
            lastKey = newKey;
            lastPtr = newPtr;
        }
        else /*If keys in node are maximum and position of node to be inserted
               is not last*/
        {
            lastKey = ptr->keys[M-2];
            lastPtr = ptr->p[M-1];
            for (i=M-2; i>pos; i--)
            {
                ptr->keys[i] = ptr->keys[i-1];
                ptr->p[i+1] = ptr->p[i];
            }
            ptr->keys[pos] = newKey;
            ptr->p[pos+1] = newPtr;
        }
        splitPos = (M - 1)/2;
        (*upKey) = ptr->keys[splitPos];

        (*newnode)=malloc(sizeof(struct node));/*Right node after split*/
        ptr->n = splitPos; /*No. of keys for left splitted node*/
        (*newnode)->n = M-1-splitPos;/*No. of keys for right splitted node*/
        for (i=0; i < (*newnode)->n; i++)
        {
            (*newnode)->p[i] = ptr->p[i + splitPos + 1];
            if(i < (*newnode)->n - 1)
                (*newnode)->keys[i] = ptr->keys[i + splitPos + 1];
            else
                (*newnode)->keys[i] = lastKey;
        }
        (*newnode)->p[(*newnode)->n] = lastPtr;
        return InsertIt;
    }/*End of ins()*/

    void display(struct node *ptr, int blanks)
    {
        if (ptr)
        {
            int i;
            for(i=1;i<=blanks;i++)
                printf(" ");
            for (i=0; i < ptr->n; i++)
                printf("%d ",ptr->keys[i]);
            printf("\n");
            for (i=0; i <= ptr->n; i++)
                display(ptr->p[i], blanks+10);
        }/*End of if*/
    }/*End of display()*/

    void search(int key)
    {
        int pos, i, n;
        struct node *ptr = root;
        printf("Search path:\n");
        while (ptr)
        {
            n = ptr->n;
            for (i=0; i < ptr->n; i++)
                printf(" %d",ptr->keys[i]);
            printf("\n");
            pos = searchPos(key, ptr->keys, n);
            if (pos < n && key == ptr->keys[pos])
            {
                printf("Key %d found in position %d of last dispalyednode\n",key,i);
                return;
            }
            ptr = ptr->p[pos];
        }
        printf("Key %d is not available\n",key);
    }/*End of search()*/

    int searchPos(int key, int *key_arr, int n)
    {
        int pos=0;
        while (pos < n && key > key_arr[pos])
            pos++;
        return pos;
    }/*End of searchPos()*/

    void DelNode(int key)
    {
        struct node *uproot;
        enum KeyStatus value;
        value = del(root,key);
        switch (value)
        {
            case SearchFailure:
                printf("Key %d is not available\n",key);
                break;
            case LessKeys:
                uproot = root;
                root = root->p[0];
                free(uproot);
                break;
        }/*End of switch*/
    }/*End of delnode()*/

    enum KeyStatus del(struct node *ptr, int key)
    {
        int pos, i, pivot, n ,min;
        int *key_arr;
        enum KeyStatus value;
        struct node **p,*lptr,*rptr;

        if (ptr == NULL)
            return SearchFailure;
        /*Assigns values of node*/
        n=ptr->n;
        key_arr = ptr->keys;
        p = ptr->p;
        min = (M - 1)/2;/*Minimum number of keys*/

        pos = searchPos(key, key_arr, n);
        if (p[0] == NULL)
        {
            if (pos == n || key < key_arr[pos])
                return SearchFailure;
            /*Shift keys and pointers left*/
            for (i=pos+1; i < n; i++)
            {
                key_arr[i-1] = key_arr[i];
                p[i] = p[i+1];
            }
            return --ptr->n >= (ptr==root ? 1 : min) ? Success : LessKeys;
        }/*End of if */

        if (pos < n && key == key_arr[pos])
        {
            struct node *qp = p[pos], *qp1;
            int nkey;
            while(1)
            {
                nkey = qp->n;
                qp1 = qp->p[nkey];
                if (qp1 == NULL)
                    break;
                qp = qp1;
            }/*End of while*/
            key_arr[pos] = qp->keys[nkey-1];
            qp->keys[nkey - 1] = key;
        }/*End of if */
        value = del(p[pos], key);
        if (value != LessKeys)
            return value;

        if (pos > 0 && p[pos-1]->n > min)
        {
            pivot = pos - 1; /*pivot for left and right node*/
            lptr = p[pivot];
            rptr = p[pos];
            /*Assigns values for right node*/
            rptr->p[rptr->n + 1] = rptr->p[rptr->n];
            for (i=rptr->n; i>0; i--)
            {
                rptr->keys[i] = rptr->keys[i-1];
                rptr->p[i] = rptr->p[i-1];
            }
            rptr->n++;
            rptr->keys[0] = key_arr[pivot];
            rptr->p[0] = lptr->p[lptr->n];
            key_arr[pivot] = lptr->keys[--lptr->n];
            return Success;
        }/*End of if */
        if (pos > min)
        {
            pivot = pos; /*pivot for left and right node*/
            lptr = p[pivot];
            rptr = p[pivot+1];
            /*Assigns values for left node*/
            lptr->keys[lptr->n] = key_arr[pivot];
            lptr->p[lptr->n + 1] = rptr->p[0];
            key_arr[pivot] = rptr->keys[0];
            lptr->n++;
            rptr->n--;
            for (i=0; i < rptr->n; i++)
            {
                rptr->keys[i] = rptr->keys[i+1];
                rptr->p[i] = rptr->p[i+1];
            }/*End of for*/
            rptr->p[rptr->n] = rptr->p[rptr->n + 1];
            return Success;
        }/*End of if */

        if(pos == n)
            pivot = pos-1;
        else
            pivot = pos;

        lptr = p[pivot];
        rptr = p[pivot+1];
        /*merge right node with left node*/
        lptr->keys[lptr->n] = key_arr[pivot];
        lptr->p[lptr->n + 1] = rptr->p[0];
        for (i=0; i < rptr->n; i++)
        {
            lptr->keys[lptr->n + 1 + i] = rptr->keys[i];
            lptr->p[lptr->n + 2 + i] = rptr->p[i+1];
        }
        lptr->n = lptr->n + rptr->n +1;
        free(rptr); /*Remove right node*/
        for (i=pos+1; i < n; i++)
        {
            key_arr[i-1] = key_arr[i];
            p[i] = p[i+1];
        }
        return --ptr->n >= (ptr == root ? 1 : min) ? Success : LessKeys;
    }/*End of del()*/

可能是什么问题？

Answer 1

在不确切知道这应该如何工作的情况下，我可以说你是在 p 之外编写的。 vector 上

    for (i=0; i < rptr->n; i++)
    {
        lptr->keys[lptr->n + 1 + i] = rptr->keys[i];
        // When you delete key 84, rptr->n is 4 at one point which takes you outside 
        // p[M] 
        lptr->p[lptr->n + 2 + i] = rptr->p[i+1]; 
    }

Valgrind是一个很好用的工具，我通过valgrind -v --leak-check=full <your executable>发现了这个问题