I am making an array with a linked list in it and I am trying to get rid of memory leaks and uninitialised values. Valgrind reports

" Conditional jump or move depends on uninitialised value(s) "

Does anyone know why this is?

Here is my code:

#include<iostream>
#include<string>
using namespace std;

struct Item
{
    int key;
    string value;
    Item *next;
};

//array for storing items and lists of items 
//- allocate array  
//- create a linked list at array index if needed
Item **items = new Item*[3];

void add_item(int key, string value, int index)
{
    
    //create new item
    Item *it = new Item;
    it->key = key;
    it->value = value;
    it->next = NULL;

    //if there are no items at location
    if(items[index] == NULL)
        items[index] = it;
    //if there is, iterate through linked list and add item at end
    else
    {
        Item* curr = items[index]; //start of linked list

        while(curr->next != NULL)
            curr = curr->next;

        curr->next = it;
    }
}

int main()
{

    Item *curr;

    add_item(1, "Happy", 0);
    add_item(2, "Sad", 0);
    add_item(3, "Laughing", 1);
    add_item(4, "Angry", 2);

    for(int i=0; i<3; i  )
    {
        curr = items[i];

        while(curr != NULL)
        {
            cout<<curr->key<<" "<<curr->value;
            curr = curr->next;
            if(curr != NULL)
                cout<<" --> ";
            else
                cout<<endl;
        }
    }

    //delete memory
    for(int i=0; i<3; i  )
    {
        curr = items[i]; //start of list

        //delete linked list starting at array index
        while(curr != NULL) 
        {
            Item *temp = curr;
            curr = curr->next;
            delete temp;
        }
        
    }
    delete [] items; //delete array 

    return 0;
}

I have rewritten the program several times and I honestly have no idea why it says that.

CodePudding user response：

Item **items = new Item*[3]; creates an array of 3 uninitialized pointers. So, the check if(items[index] == NULL) might not be true in the first call. The random value will make the program crash at while(curr->next != NULL).

You can fix it by initializing the pointer: Item **items = new Item*[3]();. The () in the end default initializes the values (e.g., to nullptr in this case).

After that the address sanitizer does not complain anymore: https://godbolt.org/z/3xxzYa4Gs