Pointer disappeared after passing to some functions (even with malloc) - c

Question

My problem is that I created a pointer at the bottom Main.
Main will call load() to read input from a dictionary and insert the words in a inputfile into a TRIE *dict by calling insert() and getnode(). However, after load() return true, the *dict lost all of the value and I cannot get what I expected(i.e. showing cat is present as it is in my dictionary input file).
I have read from other websites that pointers can retain its value after doing malloc. So I have malloced for the *dict. Please kindly let me know why the value disappeared.
#include <stdio.h>
#include <stdbool.h>
#include <stdlib.h>
#include <string.h>
#define CHAR_TO_INDEX(c) ((int)c - (int)'a')
#define ARRAY_SIZE(a) sizeof(a)/sizeof(a[0])
struct dict
{
char words[46];
struct dict* dictPath[26];
bool isEndOfWord;
};
// Returns new trie node (initialized to NULLs)
struct dict *getNode(void)
{
struct dict *pNode = NULL;
pNode = (struct dict *)malloc(sizeof(struct dict));
if (pNode)
{
int i;
for (i = 0; i < 26; i++)
pNode->dictPath[i] = NULL;
}
return pNode;
}
void insert(struct dict *root, const char *key)
{
int level;
int length = strlen(key);
int index;
struct dict *pCrawl = root;
for (level = 0; level < length; level++)
{
index = CHAR_TO_INDEX(key[level]);
if (!pCrawl->dictPath[index])
{
pCrawl = malloc(sizeof(struct dict));
pCrawl->dictPath[index] = getNode();
}
printf("%i\n",index);
pCrawl = pCrawl->dictPath[index];
}
// mark last node as leaf
pCrawl->isEndOfWord = true;
}
// Returns true if key presents in trie, else false
bool search(struct dict *root, const char *key)
{
int level;
int length = strlen(key);
int index;
struct dict *pCrawl = root;
for (level = 0; level < length; level++)
{
index = CHAR_TO_INDEX(key[level]);
if (!pCrawl->dictPath[index])
{
return false;
}
pCrawl = pCrawl->dictPath[index];
}
return (pCrawl != NULL && pCrawl->isEndOfWord);
}
bool load(struct dict *root, char *inputfile){
// open the dictionary file
FILE *infile = fopen(inputfile,"r");
int dictchar;
char tmpword[46];
int cnt = 0;
root = getNode();
// start iterating to read char
do
{
// read the character
dictchar = fgetc(infile);
if (dictchar != '\n')
{
// assign the dictionary character to a tmpword. tmpword will be used to fit into TRIES later
tmpword[cnt] = dictchar;
cnt ++;
}
// if the character is '\n', fit tmpword into TRIES
else
{
tmpword[cnt] = '\0';
cnt = 0;
for (int i = 0; i < ARRAY_SIZE(tmpword); i++)
insert(root, tmpword);
}
} while (dictchar != EOF);
return true;
}
int main (int argc, char *argv[]){
if (argc != 2)
{
return 1;
}
struct dict *root = malloc(sizeof(struct dict));
load(root, argv[1]);
char output[][32] = {"Not present in trie", "Present in trie"};
printf("%s --- %s\n", "cat", output[search(root, "cat")] );
return 0;
}
p.s. I took reference from https://www.geeksforgeeks.org/trie-insert-and-search/

Answer 1

In you function,
bool load(struct dict *root, char *inputfile)
you pass a root pointer, but then replace it with the result of getNode.
The calling code will not see this change.
You need to pass a pointer to the root pointer,
bool load(struct dict **root, char *inputfile)
for the calling code to see the change.
More simply, since you throw away the root with
root = getNode();
right near the top of the function, you could change the load signature:
struct dict * load(char *inputfile)
Instead of return true; at the end, return root; instead.
You don't have a path returning flase anyway.
Change the calling code too.
Instead of
struct dict *root = malloc(sizeof(struct dict));
load(root, argv[1]);
try this:
struct dict *root = load(argv[1]);