CODEWITHSUNDEEP
cmemory-managementstructlinked-listexc-bad-access
Melvin
Melvin

Reputation: 449

C: Linked list bad access of memory

I have to work on linked lists and get a bad access error even before something happens in my main. I don't know what's wrong. I am relatively new to dynamic memory management. It would be nice if someone could take a look on the functions. The declaration was given by the professor, so we have to return a DoubleNote*. My code is below:

#include <stdio.h>
#include <stdlib.h>

typedef struct node{

    double var;

    struct node *next;


} DoubleNode;


DoubleNode* insertFirst(DoubleNode* head, double d){

    DoubleNode* new_head;
    new_head = (DoubleNode*)malloc(sizeof(DoubleNode));

    if (new_head == NULL) {
        printf("Error: Allocating memory for new node failed!");
        exit(1);
    }

    new_head->var = d;

    new_head->next = head;

    head = new_head;


    return head;

}



DoubleNode* inserLast(DoubleNode* head, double d){

    DoubleNode* current = head;

    while (current != NULL) {
        current = current->next;
    }

    current->next = (DoubleNode*)malloc(sizeof(DoubleNode));
    if (current->next == NULL) {
        printf("Error: Allocating memory for new node failed!");
        exit(1);
    }
    current->next->var = d;
    current->next->next = NULL;

    return head;

}

DoubleNode* inverseDoubleListCon(DoubleNode* head){

    DoubleNode* current = head; // iteration variable starts on head of old list
    DoubleNode* conHead = current; // Head of the new list

    while (current != NULL) {

        current = current->next; //iteration step

        DoubleNode* newConHead = (DoubleNode*)malloc(sizeof(DoubleNode)); //allocating memory for new head

        if (newConHead == NULL) {
            printf("Error: Allocating memory for new node failed!");
            exit(1);
        }

        newConHead = current; // new_head is the next variable in the old list

        newConHead->next = conHead; //new head points to old head of the new list

        conHead = newConHead; // new head is set
    }


    return conHead;

}

void printList(DoubleNode* head){

    DoubleNode* current = head;

    while (current != NULL) {
        printf("%lf\n", current->var);
        current = current->next;
    }

}




int main(){

    DoubleNode* head = NULL;
    DoubleNode* inverseHead = NULL;
    double d;
    int i;
    int sizeOfList;

    printf("Insert amount of variables: \n");
    scanf("%d", &sizeOfList);

    for (i = 0; i < sizeOfList; i++) {
        printf("Insert variable for node [%d]: \n", i);
        scanf("%lf", &d);

        head = insertFirst(head, d);
    }

    printList(head);

    inverseHead = inverseDoubleListCon(head);

    printList(inverseHead);



    return 0;
}

Upvotes: 1

Views: 349

Answers (1)

Rishikesh Raje
Rishikesh Raje

Reputation: 8614

Firstly sizeOfList is not initalised. You need to add code to get the value of the size from the user.

You are also not updating the value of the head pointer from the insertFirst function. The code below should help.

DoubleNode* head= NULL;

// Code to get the value of sizeofList

for (i = 0; i < sizeOfList; i++)
{
   ...
    head = insertFirst(head, d);
}

The reverse function is overly complicated. You are allocating memory in newConHead which is not required for reversing a linked list.

I would suggest a rewrite along the lines of How to reverse a singly linked list using only two pointers? or http://www.geeksforgeeks.org/write-a-function-to-reverse-the-nodes-of-a-linked-list/

Upvotes: 1

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