Question

I am getting a “Segmentation fault (core dumped)” run-time error with the following code:

#include <iostream>
#include "Student.h"
#include "SortedList.h"

using namespace std;

#define BOUNDS 100

int main() {

    SortedList *list = new SortedList();  // points to the sorted list object
    Student *create[BOUNDS];  // array to hold 100 student objects
    int num = 100000;   // holds different ID numbers

    // fills an array with 100 students of various ID numbers
    for (int i = 0; i < BOUNDS; i++) {
        create[i] = new Student(num);
        num += 10;
    }

    // insert all students into the sorted list
    for (int i = 0; i < BOUNDS; i++)
    list->insert(create[i]);

    // individually deletes each student
    num = 100000;
    for (int i = 0; i < BOUNDS; i++) {
        delete list->find(num);
    num += 10;
    }

    // insert all students into the sorted list
    for (int i = 0; i < BOUNDS; i++)
    list->insert(create[i]);

    num = 100000;
    for (int i = 0; i < BOUNDS; i++) {
    list->remove(num);
    num += 10;
    }

    cout << "test2" << endl;
    delete list;
    return 0;
}

I have narrowed the error down to the delete list; lines (or whichever one comes first). I am just wondering as to why this is and how to possibly fix it. Any insight on this matter would be useful.

Answer 1

You have two problems that I can see.

First, in this loop:

for (int i = 0; i < BOUNDS; i++) {
    x = new Student(num);
    num += 10;
}

You are creating a bunch of dynamic Students and putting the latest one in x and the previous one is lost. This creates 100 Students dynamically and 99 of them are leaked. Also it doesn’t fill an array with Students like the comment above it says it does. I’m not sure what you’re trying to do here so I can’t comment on what you need to do instead.

Secondly, you are calling delete here:

delete list->find(num);

on Students that are in automatic storage (the stack) (because you filled the list with pointers to the Students in create which holds automatic Students), which leads to undefined behaviour and is probably the cause of your segfault. You don’t need to deallocate these Students because they will be deallocated when the array goes out of scope at the end of main.