CODEWITHSUNDEEP
carrayslistmalloc
Euro Pe
Euro Pe

Reputation: 73

Delete element from double linked list in c

I have a double linked list, here's structure I used:

struct list_el{
    struct data* val;
    struct list_el* next;
    struct list_el* prev;
};

struct list{
    struct list_el* head;
    struct list_el* tail;
};

When I do it like this, everything works correctly, insert and delete functions are working as I wanted:

int main(){
    struct data d1 = {"Name1","Surname1"};
    struct data d2 = {"Name2","Surname2"};
    struct data d3 = {"Name3","Surname3"};
    struct data d4 = {"Name4","Surname4"};
    struct list *l = create();
    struct list_el *el1, *el2, *el3, *el4;
    el1 = create_elem(&d1);
    el2 = create_elem(&d2);
    el3 = create_elem(&d3);
    el4 = create_elem(&d4);
    insert (l, el1);
    insert (l, el2);
    insert (l, el3);
    insert (l, el4);
    del_el(l, el1);
}

The problem is when I want to do it on arrays:

struct data arr_data[4]={{"Name1","Surname1"},{"Name2","Surname2"},{"Name3","Surname3"},{"Name4","Surname4"}};

struct list_el arr_el[4];

int main(){    
    struct list *l = create_l();
    for (int i=0; i<4; i++) {
         arr_el[i] = *create_elem(&arr_data[i]);
         insert_l(l, &arr_el[i]);
    }   
    //Till now everythink works correctly

    //Here's the problem
    del_el(l, &arr_el[0]);
}

When I run it it shows me an error: 

malloc: *** error for object 0x10002dfb0: pointer being freed was not allocated

Don't know why it happened. In create_elem() I use malloc. Any ideas?

Upvotes: 0

Views: 61

Answers (1)

dbush
dbush

Reputation: 224927

You're trying to free one of the elements of arr_el. These were not allocated by malloc, so you can't free them.

What you're doing is dereferencing the pointer returned by create_elem and copying the values it contains into an element of arr_el. This also means you have a memory leak.

You should instead declare arr_el as an array of pointers:

struct list_el *arr_el[4];

Then you assign the return value of create_elem directly to one of these:

arr_el[i] = create_elem(&arr_data[i]);
insert_l(l, arr_el[i]);

And you can then subsequently delete them:

del_el(l, arr_el[0]);

Upvotes: 2

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