Segmentation Fault With Pointers In Sorted Lists In C

Question

I have a function here that destroys an iterator acting on a sorted list.

void SortedListDestroyTheIterator (SortedListIteratorPtr iter) 
{
    Node pt = NULL;
    Node prev = NULL;
    SortedListIteratorPtr walk;

    walk = malloc(sizeof(struct SortedListIterator)+1);
    SortedListPtr li = iter->list;

    for(pt = li->start; pt!=NULL; pt = pt->next) //problem line of code
    {
        walk = pt->info;
        //delete
        if(walk==iter){
            if(prev==NULL){
                li->start = li->start->next;
            }
            else
            {
                prev->next = pt->next;
            }
        }
        prev = pt;
    }
    free(iter);
}

I have figured out that a segmentation fault occurs with this assignment statement: pt = li->start. Now this line of code is creating a node that points to the starting node of the list. If I type in li->start it works, but once I add the assignment pt=li->start I get a segmentation fault. I do not understand why or how to fix this.

rcgldr · Accepted Answer · 2015-10-01 02:13:59Z

1

Is Node a node or a pointer to node? If Node is a structure, then the code should be:

Node * pt = NULL;
Node * prev = NULL;

Although if this fix works, I don't understand why the compiler didn't produce an error or warning.

The example code doesn't show how Node, SortedListPtr, SortedListIterator, or SortedListIteratorPtr are defined.

I didn't check to see if there are other issues.

edited Oct 1, 2015 at 2:13

answered Sep 30, 2015 at 23:29

rcgldr

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Comments

t0mm13b · Accepted Answer · 2015-09-30 23:36:50Z

0

The line pt = NULL seems the culprit.

Look in the for loop code:

for(pt = li->start; pt!=NULL; pt = pt->next ) //problem line of code

answered Sep 30, 2015 at 23:36

t0mm13b

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1 Comment

rcgldr Over a year ago

As long as li->start != NULL, the for loop should be ok.

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