Debugging: Problem with linked list linkage - c

Question

I have a linked list implementation as follows:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define CAPACITY 128
typedef struct blob blob;
struct blob {
char text[CAPACITY];
struct blob* prev;
struct blob* next;
};
static blob* create_blob() {
blob* newBlob = malloc(sizeof(blob));
if (!newBlob) {
fprintf(stderr, "%s\n", "Malloc failed");
return 0;
}
newBlob->prev = 0;
newBlob->next = 0;
memset(newBlob->text, 0, CAPACITY);
return newBlob;
}
int insertAtTail(blob* list[static 1]) {
blob* newBlob = create_blob();
if (!newBlob) {
fprintf(stderr, "%s\n", "Malloc failed");
return 0;
}
if (!*list) {
*list = newBlob;
return 1;
}
blob* lastElement = *list;
while (lastElement->next) {
// Check if linkage until last element is okay
if (lastElement != (lastElement->next)->prev) {
fprintf(stderr, "%s\n", "The next_element->prev does not point to the current element");
} else {
fprintf(stderr, "%s\n", "Okay");
}
lastElement = lastElement->next; // Find last Blob
}
lastElement->next = newBlob;
newBlob->prev = lastElement;
return 1;
}
int reversePrintBlobs(blob const list[static 1]) {
if (!list) {
fprintf(stderr, "%s\n", "list is empty");
return 1;
}
const blob* tmp = list;
size_t blobCounter = 1;
while (tmp->next) {
blobCounter++;
tmp = tmp->next;
}
while (tmp && tmp != list) {
if ((tmp->prev)->next != tmp) {
fprintf(stderr, "%s\n", "error with the linkage");
exit(1);
}
printf("#number = %zu: %s\n", blobCounter--, tmp->text);
tmp = tmp->prev;
}
return 0;
}
When I add some blobs with the following main() function, it seems like the prev member of my struct doesn't point to the previous element. That is, there is a problem with the linkage. Can anyone point out why?
int main() {
FILE* pFile = fopen("example.txt", "r");
if (!pFile) {
perror("fopen failed\n");
return EXIT_FAILURE ;
}
fseek(pFile, 0, SEEK_SET);
blob* list = create_blob();
blob* tmp = list;
while (!feof(pFile)) {
size_t noBytesRead = fread(tmp->text, sizeof(char), CAPACITY,
pFile);
if (noBytesRead != CAPACITY && !feof(pFile)) {
fprintf(stderr, "%s\n", "File read failed");
exit(EXIT_FAILURE);
}
// Append a null terminating character in the end
tmp->text[noBytesRead] = '\0';
if (!feof(pFile) && insertAtTail(&list)) {
tmp = tmp->next;
}
}
}
On the other hand, If I use the following main() everything works fine.
int main() {
blob* list = create_blob();
insertAtTail(&list);
insertAtTail(&list);
insertAtTail(&list);
insertAtTail(&list);
insertAtTail(&list);
/* code */
return 0;
}

Answer 1

The bug has been fixed, the new main function is the following:
int main() {
FILE* pFile = fopen("example.txt", "r");
if (!pFile) {
perror("fopen failed\n");
return EXIT_FAILURE ;
}
fseek(pFile, 0, SEEK_SET);
blob* list = create_blob();
blob* tmp = list;
int blobCounter = 1;
while (!feof(pFile)) {
size_t noBytesRead = fread(tmp->text, sizeof(char), CAPACITY,
pFile);
if (noBytesRead != CAPACITY && !feof(pFile)) {
fprintf(stderr, "%s\n", "File read failed");
exit(EXIT_FAILURE);
}
// Append a null terminating character in the end
tmp->text[noBytesRead - 1] = '\0';
if (!feof(pFile) && insertAtTail(&list)) {
blobCounter++;
tmp = tmp->next;
}
}