Why does my Linked list program gives SIGSEV?

Question

I am creating a simple linked list program to insert and view the elements of LL. When I try to insert second element it gives SIGSEV, but I cannot understand why??!!

Please help me point the issue:

main.c:

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

typedef struct linkedList{
    int data;
    struct linkedList *next;
}LL;

LL *start;

int main(){

    int option = 0;
    while(1){
    printf("Enter option: \n");
    scanf("%d", &option);

    switch(option){
       case 1:
         addNode(start);
         break;
       case 2:
         readNodes(start);
         break;
       case 3:
         exit(0);
    }
    }
}

insert Node:

int addNode(LL *startNode){

    LL *temp, *node;
    int data = 0;

    printf("Enter data: ");
    scanf("%d", &data);

    if(startNode == NULL){/*Application only when the first element is inserted*/
        startNode = (LL*)malloc(sizeof(LL*));
        if(startNode == NULL){
          printf("Error: Memory not allocated!!\n");
          exit(1);
        }
        startNode->data = data;
        startNode->next = NULL;
        start = startNode;

        return 0;
    }

    temp = startNode;

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

    node = (LL*)malloc(sizeof(LL*));
    node->data = data;
    node->next = NULL;

    temp->next = node;

    temp = temp->next;

    return 0;
}

[In C you should not cast the result of `malloc`.](http://stackoverflow.com/questions/605845/do-i-cast-the-result-of-malloc) — Some programmer dude, Oct 16 '14 at 10:20
As for your problem, *use a debugger*. The debugger will help you find out *where* the crash is, as well as help you figure out what caused it. — Some programmer dude, Oct 16 '14 at 10:21
@JoachimPileborg Yes I used it. The error is at line "temp->next = node;" but I can't understand why — Amrit, Oct 16 '14 at 10:22
`malloc(sizeof(LL*))` --> `malloc(sizeof(LL))` and `temp->next = node;` is `(NULL)->next = node;` , `while(temp != NULL){` --> `while(temp->next != NULL){` — BLUEPIXY, Oct 16 '14 at 10:23
@BLUEPIXY Got it! Thanks so much! Plz post it as an answer, I will accept it. — Amrit, Oct 16 '14 at 10:29

score 2 · Accepted Answer · edited Oct 16 '14 at 11:06

2

sizeof takes length of structure , you always pass 4 bytes in your case for 32 bit architecture
your while loop for iterating temp node is wrong , you should rather check for next node to be NULL.

edited Oct 16 '14 at 11:06

David Ranieri

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answered Oct 16 '14 at 10:39

Bankelaal

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Why does my Linked list program gives SIGSEV?

1 Answers1