Problems in data structure - c

Question

I'm making a data structure that stores strings from a file in memory. The struture is:
typedef struct node
{
bool end;
struct node *letters[27];
} node;
Each char from the string goes through a hash function:
int
hash(int letter)
{
int n;
// converts upper case to a number from 1 to 26
if (letter >= 65 && letter <= 90)
n = letter - 64;
// converts letter case to a number from 1 to 26
else if (letter >= 97 && letter <= 122)
n = letter - 96;
// converts apostrophe to 27
else if (letter == '\'')
n = 0;
return n;
}
Thus, the structure is similar to a tree where the position of each pointer in the array corresponds to a letter, as follows:
tree
The function that loads the words into memory is as follows:
bool
load(const char *dict)
{
// open the dictionary file
FILE *infile = fopen(dict, "r");
if (infile == NULL)
{
return false;
}
// pointer for the first tree
node *first = calloc(28, sizeof(node));
if (first == NULL)
return false;
//pointer to the nodes
node *nextptr = NULL;
// word storage variables
int index = 0;
char word[LENGTH+1];
// stores the words of the file in the struct
for (int c = fgetc(infile); c != EOF; c = fgetc(infile))
{
// reads only letters and apostrophes
if ((c >= 65 && c <= 90) || (c >= 97 && c <= 122) || (c == '\''))
{
word[index] = c;
// creates a new tree from the first tree
if (index == 0)
{
// checks if there is a struct for the char
if (first->letters[hash(word[0])] != NULL)
{
nextptr = first->letters[hash(word[0])];
index++;
}
// creates a new struct for the char
else
{
first->letters[hash(word[0])] = calloc(28, sizeof(node));
if (first->letters[hash(word[0])] == NULL)
return false;
nextptr = first->letters[hash(word[0])];
index++;
}
}
// create the following structures
else
{
// checks if there is a struct for the char
if (nextptr->letters[hash(word[index])] != NULL)
{
nextptr = nextptr->letters[hash(word[index])];
index++;
}
// creates a new struct for the char
else
{
nextptr->letters[hash(word[index])] = calloc(28, sizeof(node));
if (nextptr->letters[hash(word[index])] == NULL)
return false;
nextptr = nextptr->letters[hash(word[index])];
index++;
}
}
}
// creates the last struct for a word
else if (c == '\n')
{
// ends the word
word[index] = '\0';
// the boolean end is set to true, defining the end of the word
nextptr->end = true;
nextptr = NULL;
// prepares for a new word
index = 0;
}
}
return true;
}
The function that has an error is an function that check strings and verify if is in the structure:
bool
check(const char *word)
{
node *checkptr = first;
for (int i = 0; i < sizeof(word); i++)
{
if (word[i] == '\0' && checkptr->end == true)
return true;
else if (checkptr->letters[hash(word[i])] != NULL)
checkptr = checkptr->letters[hash(word[i])];
else
return false;
}
return false;
}
When the program is started, segmentation fault occurs on the line else if (checkptr->letters[hash(word[i])] != NULL) and valgrind shows Invalid read of size 8.
I will still create a function to give the necessary free but I guess that the problem is there, mainly because I tried to check if the checkptr pointer was really set to the same structure as the first, but I discover that first is set to NULL, why?
Sorry for my bad english, i'm a beginner programmer and it's my first time on Stack Overflow, but I really don't know how to solve this. If someone can help me in any way, i thank you in advance.

Answer 1

The problem was solved. The error really was in the pointer first. I had accidentally used calloc for a new pointer, instead of the original first, so check was accessing the original first pointer (which had remained NULL).