CODEWITHSUNDEEP
c++linked-listsegmentation-faultfault
larman
larman

Reputation: 45

I keep getting segmentation fault on link list

This program is supposed to make a random linked list of n numbers that the user inputs, but when it tries to print the linked list it gets a segmentation fault.

The program works until it has to display the linked list.

#include <iostream>

class node
{
public:
    // TYPEDEF
    typedef double value_type;

    // CONSTRUCTOR
    node(
         const value_type& init_data = value_type(),
         node* init_link = NULL
         )
    { data_field = init_data; link_field = init_link; }

    // Member functions to set the data and link fields:
    void set_data(const value_type& new_data) { data_field = new_data; }
    void set_link(node* new_link)             { link_field = new_link; }

    // Constant member function to retrieve the data:
    value_type data() const { return data_field; }

    // Constant member functions to retreive the link:
    node* linker() const          { return link_field; }

private:
    value_type data_field;
    node* link_field;
};

int myrand(int)
{
    return(1 + rand() %(1000 - 1 +1));
}

void print_linked_list(node*& head_ptr, node*& print_ptr, size_t n)
{
    for (size_t i =1 ; i <= n ; i++) {
        head_ptr = new node(myrand(n), head_ptr);
    }
    std::cout << "Unsorted List: " << std::endl;
    for (print_ptr = head_ptr; print_ptr !=NULL; print_ptr = print_ptr->linker()) {
        std::cout <<  print_ptr->data() << " ";
    }
}

int main()
{
    size_t n;
    srand(time(NULL));

    node* head_ptr;
    node* print_ptr;

    std::cout << "Please input a number" << std::endl;
    std::cin >> n;

    print_linked_list(head_ptr, print_ptr, n);

    return 0;
}

Upvotes: 3

Views: 46

Answers (2)

Sam Varshavchik
Sam Varshavchik

Reputation: 118300

head_ptr is not initialized to NULL.

As such, the first node that gets created will get a garbage pointer for its link_field.

As such, when your print code attempts to walk the link list, it will eventually hit the garbage pointer, and go waltzing off into never-never land.

Upvotes: 3

Kyle A
Kyle A

Reputation: 980

You are trying to access an uninitialized pointer. You give the print_linked_list function the head_ptr variable, which is uninitialized. It then uses that value as the pointer to the next node when creating the first node. This means the condition print_ptr != NULL is never met.

This can be fixed by setting head_ptr to NULL when you declare it in main.

Upvotes: 3

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