pset5 Why can't I create the root node for my trie?

Question

The only code I have added to the top of my dictionary.c is this

#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>

#include "dictionary.h"

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

 // Structure of trie
typedef struct node
{
    bool is_word;
    struct node* children[27];
}
node;

// Vaiables used for the trie
node* root = malloc(sizeof(node));
node* triepointer = root;

However, the compiler tells me that malloc doesn't work as initializer element is not a compile-time constant.

What does the error mean? (googled and it seems that I need to use a constant here, but which part of this line is missing a constant and why?) Also, I see that Zamyla's guide doesn't use malloc when creating the root node. How can root be used if memory isn't allocated for it?

Answer 1

You declare node* root; in dictionary.h, but you can't malloc memory for it until you're in dictionary.c. However, by declaring it in your header file, you can use it across all your relevant functions, which is necessary for proper trie implementation.