CODEWITHSUNDEEP
cvisual-studio-2010
tomdavies
tomdavies

Reputation: 1976

Linked list - access violation... Where?

I'm trying to implement a linked list in C:

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

typedef struct el{
    int number;
    struct el *next;
} linkedlist;

linkedlist* newel(){
    linkedlist *newelement = (linkedlist*)malloc(sizeof(linkedlist));
    newelement->number = 10;
    newelement->next=NULL;
    return newelement;
}

void add(linkedlist **head, linkedlist *item){
    if(!*head){
        *head = item;
    }
    else{
        item->next = *head;
        *head = item;
    }
}

void prnt(linkedlist *head){
    while(head!=NULL){
        printf("%d\n", head->number);
        head=head->next;
    }
}

int main(){

    linkedlist *hd;
    add(&hd,newel());
    add(&hd,newel());
    add(&hd,newel());
    prnt(hd);

    system("PAUSE");

    return 0;
}

and I get:

Unhandled exception at 0x010c14e9 in test.exe: 0xC0000005: Access violation reading location 0xcccccccc.

I tried to debug and the problem is in prnt function. It seems it doesn't see NULL when head points to the last element... it's just going ahead. I have no idea how to fix it for now.

Upvotes: 1

Views: 279

Answers (3)

Arun
Arun

Reputation: 20383

I think the cause of exception is that hd is an uninitialized variable. In your environment, it seem to be carrying the value 0xcccccccc. The check if(!*head) probably never evaluated to be`true.

Upvotes: 1

Mani
Mani

Reputation: 17585

linkedlist *hd; This may lead to error. Because initially it may have some garbage value. so you have to NULL to head linkedlist *hd = NULL;

Upvotes: 2

dan
dan

Reputation: 1002

In your main function, initialize:

linkedlist *hd = NULL;

Upvotes: 4

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