Tries : why malloc error came

Question

I keep getting error when running my tries program.

a.out: malloc.c:2372:sysmalloc: Assertion `(old_top == (((mbinptr) (((char *) &((av)->bins[((1) - 1) * 2])) - __builtin_offsetof (struct malloc_chunk, fd)))) && old_size == 0) || ((unsigned long) (old_size) >= (unsigned long)((((__builtin_offsetof (struct malloc_chunk, fd_nextsize))+((2 *(sizeof(size_t))) - 1)) & ~((2 *(sizeof(size_t))) - 1))) && ((old_top)->size & 0x1) && ((unsigned long) old_end & pagemask) == 0)' failed.

My code is :

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

typedef struct nodeData
{
    char ch;                /* This structure looks like a linked list */
    struct nodeData *next;
}node;

typedef struct tries
{
    node *start[26];
}tries;

tries *makeAllNull(tries *root)
{
    int i=0;
    for(i=0;i<=26;i++)
    {
        root->start[i] = NULL;
    }
   return root;
}

/* Insert the given string in to the tries */
tries *insert(tries *root,char *str,int len)
{
    int i=0;
    tries *temp;
    temp = (tries *)malloc(sizeof(tries));
    while(i<len)
    {
        int k = str[i] - 'a';
        temp->start[k] = (node *)malloc(sizeof(struct nodeData));
        temp->start[k]->ch = str[i];
        temp->start[k]->next = NULL;
        if(temp->start[k] == NULL)
        {
            root->start[k] = temp->start[k];
        }
        else{
                root->start[k]->next = temp->start[k];
            }
        i++;

    }
    return root;
}

int main()
{
    int i=0;
    tries *root;
    root = (tries *)malloc(sizeof(node *));
    makeAllNull(root);
    char str[30];
    while(i<5)
    {
        scanf("%s",str);
        root = insert(root,str,strlen(str));
    }
    return 0;
}

Answer 1

Your if(temp->start[k] == NULL) is almost always false after malloc which leads to dereference NULL pointer at this line

root->start[k]->next = temp->start[k];

And this corrupts the memory.

Did you mean if(root->start[k] == NULL) instead of if(temp->start[k] == NULL)?