在 C-pset5 cs50 中加载 trie 数据结构

Question

我无法将数据加载到我的 trie 结构中。我不断收到一个分段错误。这与我的malloc有关吗？有人发现有什么问题吗？

谢谢

/**
 * dictionary.c
 *
 * Computer Science 50
 * Problem Set 5
 *
 * Implements a dictionary's functionality.
 */

#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <string.h>
#include "dictionary.h"


#define ASCII_OFFSET 97;

/** Node of the data structure used to store the dictionary key words
 * Data Structures Type is Tries
 * Includes a bool to indicate if the current node is the end of a word
 * A pointer to the nodes child node
 */
typedef struct node
{
    bool is_word;
    struct node* children[27];
}
node;
node* rootNode;
node* nextNode;

//Variable to track the size of the dictinoary
int wordCount = 0;

/**
 * Returns true if word is in dictionary else false.
 */

bool check(const char* word)
{
    //Get words length
    int wordLength = strlen(word);

    for(int i = 0; i < wordLength; i++)
    {
        //taking the character we need to check
        int charToCheck = tolower(word[i]) - ASCII_OFFSET;

        //Checking to see if the char exists in the data strucutre, Trie;
        if(nextNode->children[charToCheck] == NULL)
        {
            return false;
        }

        //Advance the next node down the trie
        nextNode = nextNode->children[charToCheck];
    }

    nextNode = rootNode;
    //Return what is_word return
    return nextNode->is_word;
}

/**
 * Loads dictionary into memory.  Returns true if successful else false.
 */

bool load(const char* dictionary)
{
    //Open dict.. file to read 
    FILE* file = fopen(dictionary,"r");

    //Check if the dict.. exsists!
    if(file == NULL)
    {
        return false;
    }

    //Creating the first node in our data strucutre
    rootNode = malloc(sizeof(node));
    nextNode = rootNode;

    //Get character to store
    int character = fgetc(file) - ASCII_OFFSET;

    //Go through the dict... file 
    while(character != EOF)
    {
        //Go through each word in the file
        while(character != '\n')
        {
            //Add into our data structure
            if(nextNode->children[character] == NULL)
            {
                //Create memory inorder to insert the next node
                nextNode->children[character] = malloc(sizeof(node));
                nextNode = nextNode->children[character];
            }else {
                nextNode = nextNode->children[character];
            }

            //advance character to next
            character = fgetc(file) - ASCII_OFFSET;
        }

        //advance character to next word
        character = fgetc(file) - ASCII_OFFSET;

        //Set the last node loaded to is_word to track the end of each word
        nextNode->is_word = true;
        wordCount++;
        nextNode = rootNode;
    }


    fclose(file);
    return true;
}

/**
 * Returns number of words in dictionary if loaded else 0 if not yet loaded.
 */

unsigned int size(void)
{
    return wordCount;
}

/**
 * Unloads dictionary from memory.  Returns true if successful else false.
 */

bool unload(void)
{
    for(int i = 0; i < 26; i++)
    {
        if(nextNode->children[i] != NULL)
        {
            nextNode = nextNode->children[i];
            unload();
        }
    }

    free(nextNode);
    return true;
}

Answer 1

1. 在将 char 用作数组中的索引之前，您不会检查它是否在范围内。任何超出 a-z 范围的字符都会导致缓冲区溢出。

2. 您将字符与已知的字符常量进行比较，您已从中减去 97。

3. 您需要通过将NULL 分配给所有数组元素并将is_word 设置为false 来初始化从malloc 返回的内存。

只是看了一眼代码，所以我可能错过了其他错误。