Question

我正在使用C来完成我的任务，它通过哈希表的方式将500字符串存储到5个字符串的字符串中，并使用链接方法来修复冲突。

哈希算法：将ASCII值相加并将模数运算符应用于结果。

哈希表存储生成的哈希密钥和指向链表的指针。如果有多个5-char字符串给出相同的散列键，则每个链表都有多个元素。

到目前为止，这是我的代码。我编译它（Codeblock），似乎没有错误。但程序崩溃了。

请提供一些关于我在哪里做错的意见。

#include <stdio.h>
#include <string.h>

#define SLEN 500
#define WLEN 5
#define MPRIME 73

struct Node {
    char s[WLEN+1];      // array to hold the 5-letter word
    int sindex;          // starting index of the word
    struct Node * next;  // a pointer to the next word in the list
};

int searchword(char *);
int hashfunc(char *);
void build_hashtbl();

struct Node * hashtable[MPRIME] = {NULL};

char string[SLEN+1] = "thenamewasfamiliartomeonseverallevelslookingbackitwasfatethatifoundhimihadcometopeppervillebeachtocloseonasmallhousethathadbeeninourfamilyforyearsonmywaybacktotheairportistoppedforcoffeetherewasafieldacrossthestreetwherekidsinpurpletshirtswerepitchingandhittingihadtimeiwanderedoverasistoodatthebackstopmyfingercurledinthechainlinkfenceanoldmanmaneuveredalawnmoweroverthegrasshewastannedandwrinkledwithahalfcigarinhismouthheshutthemowerwhenhesawmeandaskedifihadakidoutthereisaidnoheaskedwhatiwasdoing";

int main(void) {
    int index;
    char query[WLEN+1];
    build_hashtbl();      // prepare the hash table
    printf("Enter a 5-letter word to search: ");
    scanf("%s", query);
    index = searchword(query);
    if (index != -1)
        printf("The word %s starts at index %d.\n", query, index);
    else
        printf("The word %s is not found.\n", query);
    return 0;
}

int searchword(char * word) {
    int hashval;
    struct Node * lhead;
    hashval = hashfunc(word);
    lhead = hashtable[hashval];
    while (lhead) {
        if (strcmp(lhead->s,word) == 0)
            return lhead->sindex;
        lhead = lhead->next;
    }
    return -1;
}

int hashfunc(char *){
    int hashval = 0;
    int i = 0;
    for (i = 0; i < WLEN; i++){
        hashval += (int) string[i];
    }
    return (int) (hashval % MPRIME);
}

void build_hashtbl(){
    struct Node *hashtable[MPRIME]; //already declared. put here for ease
    struct Node * head = NULL;
    struct Node * last = NULL;

    int i = 0;
    int k = 0;
    int key = 0;
    char sElement[WLEN+1] = {0};

    for (i = 0; i <SLEN; i = i+WLEN){ //for every 5 char, find they hashtable index key
        key = hashfunc(*string[i]);

        for (k = 0; k <WLEN; k++){ //create a new string, sElement from the 5 letter word
        sElement[k] = string[i+k];
        }



    if (hashtable[key] != (NULL)){  //if the hashtable element at that index is empty, STORE it in a node
        hashtable[key] = head;
        struct Node *new_node;
        new_node = (struct Node *) malloc ( sizeof (struct Node) );
        strcpy(new_node->s, sElement); //put the new 5 letter word string into the node
        new_node->sindex = i; //put the starting index of this word
        new_node->next = NULL; //the next pointer is set to NULL
        head->next = new_node; //finally set the head node to point to this new node
        last = new_node; //set the new node as the last node
    }
    else { //if there is already a node in the array
        struct Node *new_node;
        new_node = (struct Node *) malloc ( sizeof (struct Node) );
        strcpy(new_node->s, sElement); //put the new 5 letter word string into the node
        new_node->sindex = i; //put the starting index of this word
        new_node->next = NULL; //the next pointer is set to NULL
        head->next = new_node; //finally set the head node to point to this new node
        last->next = new_node; //set the last node to point to thew new created node
        last = new_node; //set the new node as the last node
    }

    }
}

Answer 1

你使用过的最后一个和头部没有初始化，所以head-＆gt;接下来和朋友会发生段错误。实际上你根本不需要它们而且你不需要你的if分支 - 只需在设置new_node-＆gt;之后用new_node替换hashtable [key]，然后在hashtable [key]

旁边

void build_hashtbl(){

    int i = 0;
    int k = 0;
    int key = 0;

    char sElement[WLEN+1] = {0};

    for (i = 0; i <SLEN; i = i+WLEN){ //for every 5 char, find they hashtable index key
        key = hashfunc(string+i);

        for (k = 0; k <WLEN; k++){ //create a new string, sElement from the 5 letter word
            sElement[k] = string[i+k];
        }

        struct Node *new_node;
        new_node = (struct Node *) malloc ( sizeof (struct Node) );
        strcpy(new_node->s, sElement); //put the new 5 letter word string into the node
        new_node->next=hashtable[key];
        new_node->sindex=i;
        hashtable[key]=new_node;

    }
}

适合我。

编辑：还需要#include <stdlib.h>（至少在这里）

指向链表的指针数组

1 个答案: