CODEWITHSUNDEEP
cmemory-managementlinked-listfree
loay
loay

Reputation: 91

free a struct of a linked list that have struct nodes

I have a struct of a linked list the have a node struct inside

struct gradeNode {
char courseName[sizeName];
int grade;
struct gradeNode *next;
struct gradeNode *prev;

struct gradeList {
struct gradeNode *head;
struct gradeNode *next;

I'm trying to destroy the list free!! but i get exception of access violation any help 

void destroyList(struct gradeList *head)
{
    struct gradeNode* tmp;

    while (head!= NULL)
    {
        tmp = head;
        head = head->next;

        free(tmp);
    }

    free(head);
}

Here is the main

int i = 0;
for (i; i < numOfStuds; i++) {
    destroyList(&students[i].gradelist);
}

Upvotes: 0

Views: 211

Answers (1)

Millie Smith
Millie Smith

Reputation: 4604

void destroyList(struct gradeList *head)
{
    struct gradeNode* tmp;

    while (head!= NULL)
    {
        tmp = head; //<<<<<<< assigning a struct gradeList* to a struct gradeNode*
        head = head->next;

        free(tmp); //<<<<<<< freeing the alias
    }

You're assigning a pointer of one type to a pointer of another type and then freeing it, which is especially problematic since struct gradeList appears to be a member of struct gradeNode.

Check your warnings. Are you not getting a warning for tmp = head? With gcc 7.2 I get:

[x86-64 gcc 7.2 #1] warning: initialization from incompatible pointer type [-Wincompatible-pointer-types]

https://godbolt.org/g/EWfLCn

Upvotes: 1

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