CODEWITHSUNDEEP
c
skills
skills

Reputation: 327

Listing values from Linked list

After inserting elements to my linked list, i would like to retrieve them.

This is the struct:

typedef struct node
{
    int data;
    struct node *next;
} Element;

typedef Element* ROW;

I start my list with :

void startRow(ROW *row){
    *row = NULL;
}

After that, i use the function to insert at the end:

void insertEnd(ROW *row, int value){
    if(*row==NULL){
        *row = (ROW) (malloc(sizeof(Element)));
        if(*row==NULL){
            return;
        }else{
            (*row)->data = value;
            (**row).next = NULL;
        }
    }
}

And to list the values, i use this function (I plan on removing recursion, just playing arround):

void listValues(ROW row){
    if(row==NULL){
        return;
    }
    printf("%d\n", row->data);
    listValues(row->next);
}

I call it like this, but it only outputs the first element!

int main(){
    ROW row;

    startRow(&row);
    insertEnd(&row, 10);
    insertEnd(&row, 20);

    listValues(row);

    return 0;
}

Why? Shouldn't it output the complete list?

Upvotes: 0

Views: 53

Answers (2)

Maraboc
Maraboc

Reputation: 11083

The problem is in the method insertEnd.

You should link the elements of the list not overide them :) like this :

void insertEnd(ROW *row, int value){
    if(*row!=NULL){
        ROW *lastElement = (ROW) (malloc(sizeof(Element)));
        if(*lastElement==NULL){
            return;
        }else{
            (*lastElement)->data = value;
            (**lastElement).next = NULL;
            (**row).next = lastElement;
        }
    } else {
        *row = (ROW) (malloc(sizeof(Element)));
        if(*row==NULL){
            return;
        }else{
        (*row)->data = value;
        (**row).next = NULL;
    }
}

Like this you will link all your list elements.

Upvotes: 0

JCx
JCx

Reputation: 2769

*row is not null after the first insert. So the next insert never happens.

void insertEnd(ROW *row, int value){
    if(*row==NULL){
        printf("Inserting %d\n", value);
        *row = (ROW) (malloc(sizeof(Element)));
        if(*row==NULL){
            return;
        }else{
            (*row)->data = value;
            (**row).next = NULL;
        }
    }
}

Add a debug printf like this and it'll become obvious what's happening.

I think there are more fundamental problems though with the design!

You might want to keep a pointer to the start of the list around otherwise it'll be mighty difficult to find it again. And for a fast insert at the end you might want to keep a pointer to the end of the list as well.

I'm assuming that you are trying to figure this out for yourself, so I won't give you the answer :)

Upvotes: 3

Related Questions