Array of linked lists added to from directory - c

Question

I've been trying to create an array of linked lists. The array being size 26 each part corresponding to a letter of the alphabet. The user inputs a directory of the PC and the name of any folders or files in that directory are then added to the a linked list in the array based on what letter they start with.
How i've been trying to do it->
#include <stdio.h>
#include <string.h>
#include <dirent.h>
#include <stdlib.h>
My node and its declaration:
struct node{
char data[50];
struct node *next;
};
struct node* nodeArray[26];
My alphabet:
const char* basis[26] = {"a","b","c","d","e","f","g","h","i","j","k","l","m","n","o","p","q","r","s","t","u","v","w","x","y","z"};
A string comparing function to check which linkedlist in the array my word goes(compares to alphabet)
int StartsWith(const char *a, const char *b)
{
if(strncasecmp(a, b, strlen(b)) == 0) return 1;
return 0;
}
Where I add the node and also where the problem is(the printf("1") is there to stop my computer from basically crashing):
void addNode(struct node **q,const char *d){
if(((*q)->data)==NULL){
*q = malloc(sizeof(struct node));
strncpy((*q)->data,d,50);
(*q)->next = NULL;
} else {
(*q)->next = malloc(sizeof(struct node));
*q = (*q)->next;
printf("1");
addNode(q,d);
}
}
The function that calls addNode, directory is a computer directory that's already been checked to exist:
void returner(char* directory){
int i;
DIR *dp;
struct dirent *ep;
char* tempD;
dp = opendir (directory);
struct node **z;
while ((ep = readdir(dp))){
tempD = (char*)malloc(50);
if ( !strcmp(ep->d_name, ".") || !strcmp(ep->d_name, "..") ){
} else {
strncpy(tempD, ep->d_name, 50);
for(i=0; i<26 ; i++){
if(StartsWith(tempD, basis[i])){
z = &nodeArray[i];
addNode(z,tempD);
print();
}
}
}
free(tempD);
}
closedir (dp);
}
Print function:
void print(){
int i;
struct node *temp;
for(i=0 ; i < 26; i++){
temp = malloc(sizeof(struct node));
temp = nodeArray[i];
while(temp != NULL){
printf("%s\n",temp->data);
temp = temp->next;
}
}
}
The program seems fine when adding the first node to a spot on the array such as "aaa.txt" "bbb.txt" "ccc.txt" "ddd.txt", but once a second is attempted to be added like a "ccd.txt" after a "ccc.txt" exists when it keeps going forever or until the pc crashes

Answer 1

You're not checking the right value in your addNode for finding the list insertion point.
Pointer-to-pointer enumeration through a linked list is frequently used to walk from the head pointer to the last next pointer in the list, each time holding the address of the said-pointer. When you reach one that is NULL (which will be head in the case of an empty list), you stop, and you can use your pointer-to-pointer via dereference to assign your new node address.
If you want to insert on the tail, the way to do it would be something like this:
#define DATA_MAX_LEN 50
void addNode(struct node **q,const char *d)
{
// assumes a null-terminated linked list
while (*q)
q = &(*q)->next;
*q = malloc( sizeof **q );
// ensures truncation and termination
strncpy((*q)->data,d,DATA_MAX_LEN-1);
(*q)->data[ DATA_MAX_LEN-1] = 0;
// make sure we terminate the list at our new node
(*q)->next = NULL;
}
Invoked from your updated returner function like this:
void returner(char* directory)
{
DIR *dp = opendir (directory);
if (dp)
{
struct dirent *ep;
while ((ep = readdir(dp)))
{
// skip parent and self symbolic links
if (ep->d_name[0] == '.' && (ep->d_name[1] == 0 || (ep->d_name[1] == '.' && ep->d_name[2] == 0)))
continue;
for(int i=0; i<26 ; i++)
{
if(StartsWith(ep->d_name, basis[i]))
addNode(nodeArray+i, ep->d_name);
}
}
closedir (dp);
}
}