CODEWITHSUNDEEP
cpointerslinked-list
Dominic JL
Dominic JL

Reputation: 111

Why does this linked list Seg Fault?

The following code results in a segmentation fault if insertBefore is called after insertAfter or if insertAfter is called multiple times.

void insertBefore(list *l, void *p){
    node* newNode = malloc(sizeof(node) + l->SizeOfData);
    memcpy(newNode->item, p, l->SizeofData);
    l->curent->previous->next = newNode;
    l->current->previous = newNode;
}
void insertAfter(list *l, void *p){
    node* newNode = malloc(sizeof(node) + l->SizeOfData);
    memcpy(newNode->item, p, l->SizeofData);
    l->curent->next->previous = newNode;
    l->current->previous->next = newNode;
    l->current = newNode;
}

The lists being used are:

struct node {
    struct node *previous;
    struct node *next;
    char item[];
};

typedef struct node node;

struct list {
    node *first;
    node *current;
    node *last;
    int SizeOfData;
};

list *newList(int b) {
    list *list = malloc(sizeof(list));
    node *sentnode = malloc(sizeof(node));
    sentnode->previous = sentnode;
    sentnode->next = sentnode;
    list->first = sentnode;
    list->current = sentnode;
    list->last = sentnode;
    list->SizeOfData = b;
    return list;
}

Upvotes: 1

Views: 85

Answers (1)

Klas Lindbäck
Klas Lindbäck

Reputation: 33273

You forgot to set the previous and next pointers of newNode. There is also another bug in insertAfter (changed line).

void insertBefore(list *l, void *p){
    node* newNode = malloc(sizeof(node) + l->SizeOfData);
    memcpy(newNode->item, p, l->SizeofData);
    newNode->previous = l->current->previous;   // Added line
    newNode->next = l->current;                 // Added line
    l->current->previous->next = newNode;
    l->current->previous = newNode;
}

void insertAfter(list *l, void *p){
    node* newNode = malloc(sizeof(node) + l->SizeOfData);
    memcpy(newNode->item, p, l->SizeofData);
    newNode->previous = l->current;        // Added line
    newNode->next = l->current->next;      // Added line
    l->current->next->previous = newNode;  
    l->current->next = newNode;            // Changed line
    l->current = newNode;
}

Upvotes: 2

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