How can i free this list?

Question

Pls help me to finish a project i dont know how i can free this struct. When i use valgrind it says memory lost because i dont know ho to use free

typedef struct list{
    int value1;
    int value2;
    struct list * next;
}List;

List *first;
List *last;


void create_list(){
    List *aux;
    aux = (List *) malloc(sizeof(List));
    first= aux;
    last= first;
}     

void insert(int a, int b){
    List *aux;
    aux = (List *) malloc(sizeof(List));
    aux->value1=a;
    aux->value2=b;
    last->next=aux;
    last= last->next;
    aux->next= NULL;
}

int main(int argc, const char* argv[]){

    create_list();
    insert(1,2);


    //How can i free?

}

Possible duplicate of [How do I free memory in C?](http://stackoverflow.com/questions/9069205/how-do-i-free-memory-in-c) — Łukasz, Oct 09 '15 at 20:03
@NoOP's http://stackoverflow.com/questions/605845/do-i-cast-the-result-of-malloc — PC Luddite, Oct 09 '15 at 20:15
@Łukasz I don't think the link you mention applies here. It is about de-allocating an array (which can be done in one go), whereas the OP here needs to delete all nodes of a linked list one by one. — WhiteViking, Oct 09 '15 at 21:32

score 2 · Answer 1 · answered Oct 09 '15 at 20:03

2

How about

while(first != last) {
      List* temp = first->next;
      free(first);
      first = temp;
}
free(last);

answered Oct 09 '15 at 20:03

PC Luddite

5,883
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score 1 · Answer 2 · answered Oct 09 '15 at 20:01

1

just iterate through all the nodes by first getting the node's next, and then free the current node. When done, free the list struct itself...

answered Oct 09 '15 at 20:01

ByoTic

103
8

jayant · Answer 3 · 2015-10-09T20:27:35.277

0

You could use a recursive function like the one below.

free_list(List* input) {
    if(input == NULL)
        return;
    if(input->next == NULL) {
        free(input);
    } else {
        free_list(input->next);
        free(input);
    }
 }

edited Oct 09 '15 at 20:27

answered Oct 09 '15 at 20:04

jayant

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I tend to avoid recursion when possible. It can take up a lot of stack space, especially if it's a really big list. – PC Luddite Oct 09 '15 at 20:14
Thanks! I tried to comment on your solution regarding the ++ operator but didn't have enough reputation :( – jayant Oct 09 '15 at 20:24
1

@jayant I edited my answer almost immediately after posting it because I realized using `++` was wrong. – PC Luddite Oct 09 '15 at 20:27

How can i free this list?

3 Answers3