Question

Okay, I put together a simplified example of the problem code:

#include "stdio.h"
#include "string.h"

struct Trie{
    //Holds sub-tries for letters a-z
    struct Trie *sub[26];
    //Is this a substring, or a complete word?
    int is_word;
};
typedef struct Trie Trie;

Trie dictionary;

int main(int argc, char *argv[]){
    //A list of words
    char *words[7] = {"the","of","and","to","a","in","that"};

    //Add the words to the Trie structure
    int i=0, wordlen;
    Trie *sub_dict;
    for (;i<7; i++){
        //Reset
        printf("NEW WORD\n");
        sub_dict = &dictionary;
        //Add a word to the dictionary
        int j=0, c;
        while (c = words[i][j], c != '\0'){
            printf("char = %c\n",c);
            //Initialize the sub-Trie
            if (sub_dict->sub[c-97] == NULL)
                sub_dict->sub[c-97] = (Trie*) malloc(sizeof(Trie*));
            //Set as new sub-trie
            sub_dict = sub_dict->sub[c-97];
            j++;
        }
        sub_dict->is_word = 1;
    }
}

Basically, I have a Trie data structure that holds the letters “a” through “z”. I have a list of words that should get added inside the while loop. Unfortunately, I get a segmentation fault at different points in the loop (depending on when I run it).

I’m guessing the problem has something to do with the line
sub_dict->sub[c-97] = (Trie*) malloc(sizeof(Trie*));
but I’m new to C, so I have absolutely no clue what’s going on.

Answer 1

sub_dict->sub[c-97] = (Trie*) malloc(sizeof(Trie*));
there is an error.

sizeof(Trie*) will be 4 in 32bit os, because Trie* is a pointer, and the size of a pointer in 32bit os is 4.
you can do like this: sub_dict->sub[c-97] = (Trie*) malloc(sizeof(Trie));