Thread: error subscripted value is neither an array nor pointer nor vector

it crashes when i try to assign memory as well

Show what you tried.

however i didn't realise that linkedlist *list = null is the same as linked list *list ...... list->head = null list->tail = null

But they are not the same you have three different pointers.

Let me ask another couple of questions: What is the purpose of your list pointer in main()? Why are you trying to return list from your initialize function?

linked list holds the head and the tail points of the list. so it is like the first i had in my previous code (page 2) i need the updated list from initalize so i can pass it onto other functions like add node print list etc etc.

as to what i tried with the call to malloc i just simply commented out lines 37 and 38

as to what i tried with the call to malloc i just simply commented out lines 37 and 38

Show me exactly what you tried, just removing things is not going to solve the problem.

im clearly not understanding this.....
if i have a function int foo() it returns a type int yes?
if i have a function char foo it returns a type char
etc
if i have a unction int *foo why doesnt it return a pointer to a type int

if i change the return type to linked list and the head_temp to type linked list

Code:

#include <stdio.h>
#include <stdlib.h>

typedef struct Node
{
    int age;
    struct Node *next;
}Node;

typedef struct LinkedList
{
    struct Node *head;
    struct Node *tail;
}LinkedList;

struct LinkedList *initalize_list(LinkedList *list);
struct LinkedList *create_head(void);
struct Node *get_memory(void);
int get_age(void);
void print_list(LinkedList list);
void delete_list(LinkedList *list);

int main()
{
    //declare my list
    LinkedList *list = NULL;

    list = initalize_list(list);
    print_list(*list);
    delete_list(list);

    return 0;
}

struct LinkedList *initalize_list(LinkedList *list)
{
    //list->head = NULL;
    //list->tail = NULL;

    list->head = create_head();
    list->head->next = NULL;
    list->tail = list->head;

    list->head->age = get_age();
    return list;

}

struct LinkedList *create_head(void)
{
    LinkedList *head_tmp;

    head_tmp = get_memory();
    if (!head_tmp)
    {
        fprintf(stderr, "error allocating memory\n");
        exit(EXIT_FAILURE);// if it cant allocate memory for the head node at startup somthing really wrong so bug out
    }

    return head_tmp;
}

struct Node *get_memory(void)
{
    return malloc(sizeof(Node));
}

int get_age(void)
{
    int age;

    printf("PLease enter an age: ");
    scanf(" %d", &age);

    return age;
}

void print_list(LinkedList list)
{
    int count = 1;
    Node *tmp = list.head;

    while (tmp)
    {
        printf("person%d's age is %d\n", count, list.head->age);
        count++;
        tmp = list.head->next;
    }
}

void delete_list(LinkedList *list)
{
    int count = 1;
    Node *tmp;

    printf("freeing memory.....\n");
    while (list->head)
    {
        tmp = list->head->next;
        printf("freeing element %d\n", count);
        free(list->head);
        list->head = tmp;
        count++;
    }
    printf("memory freed\n");
}

i get the following warnings:

Code:

linked list simple/main.c|40|warning: assignment from incompatible pointer type [-Wincompatible-pointer-types]|

/linked list simple/main.c|53|warning: assignment from incompatible pointer type [-Wincompatible-pointer-types]|

broadly i have done every permitation of it that i can think of and only the one where i return a pointer of type node compiles

if i return *head_tmp i get an error

Originally Posted by laserlight

It does, but what I've noticed is that you have a bad habit of dereferencing a pointer then returning the result, so that's probably what you've been doing: returning an int when you want to return a pointer to int.

if int * foo() returns a pointer of type int.... why doesn't struct node *foo() return a pointer of type struct node

Originally Posted by laserlight

It does. I think Click_here identified the problem.

By the way, you posted an error message about incompatible types. Doesn't the error message mention the types involved? Like, didn't it say that a struct LinkedList* was expected, but a struct Node* was found, or something to that effect?

i thought click here said it returned a stuct _*

the error message i got was

Code:

linked list simple/main.c|46|error: incompatible types when returning type ‘LinkedList {aka struct LinkedList}’ but ‘struct LinkedList

Originally Posted by Click_here

Okay... Let me be more direct...

Code:

struct LinkedList *create_head(void);

... should be

Code:

struct Node *create_head(void);

Why? Because the "head" is a Node. What is a "Node"? An individual element on the list - i.e. One person's age

This means that in create_head you'll need to change the type that you "malloc" to a Node.


What you are currently doing is creating not a "head", but another struct that contains a "head" and "tail" - aka a "LinkedList"

isnt this exactly what i had in post 81