为什么我的用于将元素插入到哈希树中的C代码在Main（）中起作用，但是当我通过函数调用它时却不起作用？

Question

I'm fairly certain this has something to do with pointers and the function using copies instead, but I'm not sure how...because I've inserted the pointer as a parameter for create();

#include <stdio.h>
#include <cs50.h> 
#include <string.h>

typedef struct list {
    string word;
    struct list *next;
}
linkedList; 

struct list* create (string newWord) {
    linkedList *new = malloc(sizeof(newWord));
    new->word = newWord;
    new->next = NULL;
    return new;
}

struct list* insert (struct list *theList, string newValue) {
    linkedList *anotherOne = create(newValue);
    anotherOne->next = theList;
    return anotherOne;
}

int hash (string name) {
    return strlen(name);
}

void hashInsert (struct list *theList, string newValue) {
    theList = create(newValue);
    }

int main(void) {
   linkedList *names[24] = {NULL};
   int num = hash("heey");
 //  names[num] = create("heey"); // <- this code works when I uncomment it
   hashInsert(names[num], "heey"); // <-- this causes a segfault.. idk why
   printf("%s", names[num]->word);
}

Answer 1

Your hashInsert function creates a local copy of the pointer ( theList ), you modify said local copy, but the actual pointer in your main function is still set to NULL . Calling printf on that is the cause of your segmentation fault.

You can resolve this issue by passing a pointer to the pointer to your function

void hashInsert(string list **theList, string newValue) {
    *theList = create(newValue);
}

and then call it

hashInsert(&names[num], "heey");

This way, you modify the value of the pointer from main .

EDIT

Also, as the comments state, your malloc does indeed not allocate enough memory, you also need some memory to store the next list pointer.

Answer 2

The problem is with you hashInsert function. It takes the pointer by value (so the original pointer you pass isn't modified). There's a much better way to go about this-

struct list* hashInsert(char* string){
    return create(string);
}

A few points aside from that, don't use string , always use char* since that what it really is. I see you're using some library, but you're better off simply including the proper headers yourself, in this case, you should include stdlib.h since it contains the definition of malloc() .