Question

ok so i define my structure like this.

    struct trie {
        struct trie *child[26];
        int count;
        char letter;
    };

the problem is when i try to fill my trie with words i get a segmentation fault.
ive been told that the problem is that the child variable isn’t pointing to anything and setting them to NULL would fix this. Also creating a second structure would be a good way to achieve this. i am new to C programming and am confused on how to create a second structure to achieve this. any help would be much appreciated.

int addWordOccurrence(const char* word)
{

    struct trie *root;
    root = (struct trie *)malloc(sizeof(struct trie*));
    struct trie *initRoot=root;
    int count;

    int x=strlen(word);
    printf("%d",x);
    int i;
    for(i=0; i<x; i++)
    {  
        int z=word[i]-97;
        if(word[i]=='\n')
        {
            z=word[i-1]-97;
            root->child[z]->count++;
            root=initRoot;
        }

        root->child[z] = (struct trie *)malloc(sizeof(struct trie));
        root->child[z]->letter=word[i];
        root->child[z]=root;
    }
    return 0;
}

Answer 1

root->child[z] = (struct trie *)malloc(sizeof(struct trie));
root->child[z]->letter=word[i];
root->child[z]=root;

This is problematic.
1) What if child[z] was already set?
2) You never set child[z]->child or child[z]->count to anything

#2 is causing your segfaults, #1 is a memory leak.

My solution would be to write a function for allocating new children:

struct trie* newtrie(char newchar) {
    struct trie* r = malloc(sizeof(struct trie));
    memset(r, 0, sizeof(struct trie));
    r->letter = newchar;
    return r;
}

Then your code would become:

    if (root->child[z] == NULL)
        root->child[z] = newtrie(word[i]);
    root->child[z]=root;

You also have to change the malloc of root:

struct trie *root = newtrie(0);

Which is more clear, and avoids the errors I mentioned. http://codepad.org/J6oFQJMb No segfaults after 6 or so calls.

I’ve also noticed that your code mallocs a new root, but never returns it, so nobody except this function can ever see it. This is also a memory leak.