Segmentation fault loading dictionary into trie tree - c

Question

I'm making a program that reads a given dictionary into a trie tree, and then
performs auto complete on a string inputted by the user. When I use the dictionary file that I am required to use (~100,000 words) I get a segmentation fault. I can't seem to figure out what is causing the segmentation fault. Any help would be appreciated.
typedef struct trieTree {
int data;
struct trieTree *array[26];
}trieTree;
insert function:
trieTree* insert_tree(trieTree *t, char *s, int val)
{
int i;
trieTree *p;
if (strlen(s) == 0)
return t;
if (t == NULL)
t = new_tree(t);
p = t;
for (i = 0; i < strlen(s); ++i) {
if (p->array[s[i] - 'a'] == NULL)
p->array[s[i] - 'a'] = malloc(sizeof (trieTree));
p = p->array[s[i] - 'a'];
}
p->data = val;
return t;
}
Filling the tree:
trieTree* load_tree(trieTree *t, char *file)
{
char s[MAX];
FILE *f = fopen(file, "r");
if (f == NULL)
printf("Error! File not found.");
else
while (feof(f) == 0) {
fscanf(f, "%s", s);
t = insert_tree(t, s, 1);
}
return t;
}
Main function
int main()
{
trieTree t;
new_tree(&t);
load_tree(&t, "dict.txt");
char word[100];
printf("Enter word: ");
scanf("%s", word);
char dat[100] = "";
search_tree(&t, word, dat);
return 0;
}
trieTree* new_tree(trieTree *t)
{
int i;
t = malloc(sizeof (trieTree));
for (i = 0; i < 24; ++i)
t->array[i] = 0;
return t;
}

Answer 1

Your function new_tree() returns a pointer to allocated memory but the returned value is ignored. That's a memory leak, and your code continues to use an uninitialized variable. That's a problem!
int main()
{
trieTree t;
new_tree(&t);
load_tree(&t, "dict.txt");
…
trieTree* new_tree(trieTree *t)
{
int i;
t = malloc(sizeof(trieTree));
for (i = 0; i < 24; ++i)
t->array[i] = 0;
return t;
}
The 24 in the function should be 26, of course. But the function allocates memory and assigns it to the local pointer (original set to point to t in main(), but the malloc() zaps that value). That pointer is returned, but the return is ignored. The variable t in main() is still uninitialized, but it is passed to the load_tree() function.
Frankly, you need:
int main()
{
trieTree *tp = new_tree();
load_tree(&t, "dict.txt");
…
trieTree* new_tree(void)
{
int i;
trieTree *t = malloc(sizeof(trieTree));
if (t == 0)
{
fprintf(stderr, "memory allocation failure\n");
exit(EXIT_FAILURE);
}
for (i = 0; i < 26; ++i)
t->array[i] = 0;
return t;
}
Note that errors should be reported on the standard error channel; that is what it's for. And that every memory allocation should be checked, because if you don't check, it will fail and your program will crash.
There are probably a lot of other problems; I've not investigated them all. This should get you further before crashing.
This seems to work for me, though admittedly I only tested it on a 'dictionary' of 257 words.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
enum { MAX = 1024 };
typedef struct trieTree
{
int data;
struct trieTree *array[26];
} trieTree;
static trieTree *new_tree(void)
{
int i;
trieTree *t = malloc(sizeof(trieTree));
if (t == 0)
{
fprintf(stderr, "malloc for %zu bytes failed\n", sizeof(trieTree));
exit(EXIT_FAILURE);
}
t->data = 0;
for (i = 0; i < 26; ++i)
t->array[i] = 0;
return t;
}
static trieTree *insert_tree(trieTree *t, char *s, int val)
{
int i;
trieTree *p;
if (strlen(s) == 0)
return t;
if (t == NULL)
t = new_tree();
p = t;
int len = strlen(s);
for (i = 0; i < len; ++i)
{
if (p->array[s[i] - 'a'] == NULL)
p->array[s[i] - 'a'] = new_tree();
p = p->array[s[i] - 'a'];
}
p->data = val;
return t;
}
static trieTree *load_tree(trieTree *t, char *file)
{
char s[MAX];
FILE *f = fopen(file, "r");
if (f == NULL)
{
fprintf(stderr, "Error! File not found.");
exit(EXIT_FAILURE);
}
else
{
while (fscanf(f, "%s", s) == 1)
t = insert_tree(t, s, 1);
fclose(f);
}
return t;
}
static void print_trie(trieTree *t, char *pad)
{
int len = strlen(pad);
char space[len + 3];
memset(space, ' ', len + 2);
space[len + 2] = '\0';
for (int i = 0; i < 26; i++)
{
if (t->array[i] != 0)
{
printf("%s%c\n", pad, i + 'a');
print_trie(t->array[i], space);
}
}
}
static void free_trie(trieTree *t)
{
if (t != 0)
{
for (int i = 0; i < 26; i++)
free_trie(t->array[i]);
free(t);
}
}
int main(void)
{
trieTree *tp = new_tree();
if (tp != 0)
{
tp = load_tree(tp, "dict.txt");
print_trie(tp, "");
free_trie(tp);
}
return 0;
}
I believe it is leak free, too.
Note that this code will crash and burn if any of the input words contains any upper-case letters, or digits, or punctuation. It only handles lower-case and white space; anything else is an unchecked disaster waiting to devastate your program. That's because I've not done any substantive work in the insert_tree() function. You need to worry about 'invalid' characters in that function, probably by case-converting upper-case letters to lower-case and ignoring anything that's not a letter.