read access violation, temp was 0xDDDDDDDD - c++

Question

void deleteBasedOnID(student* head,student* tail,int stu_ID)
{
if (head == NULL)
{
std::cout << "nothing to be deleted";
}
else if (stu_ID == head->stu_ID)
{
//delete from the beginning
temp = head->next;
if (temp == NULL)
{
tail = NULL;
}
else
{
temp->prev = NULL;
}
std::cout << "Deleted ID: " << head->stu_ID << std::endl;
delete head;
head = temp;
}
else
{
//start from second
temp = head;
previous = NULL;
while (stu_ID != temp->stu_ID)
{
previous = temp;
temp = temp->next;
if (temp == NULL)
{
std::cout << "no such ID!" << std::endl;
return;
}
}
previous->next = temp->next;
if (temp->next == NULL)
{
tail = previous;
}
else
{
temp->next->prev = previous;
}
std::cout << "Deleted ID: " << temp->stu_ID << std::endl;
delete temp;
}
}
I have a student struct and global pointers head and tail, I put the said head and tail into deleteBasedOnID head and tail arguments
it works fine for if(head == NULL) or the else block but however whenever I try to delete from the beginning, it works fine internally but after I tried to display the list, error occurred.
This is my display function body
void display()
{
temp = head;
while (temp != NULL)
{
std::cout << "Student ID: " << temp->stu_ID << std::endl;
temp = temp->next;
}
}
main function
int main()
{
head = NULL;
tail = NULL;
temp = NULL;
int id;
std::cout << std::endl;
std::cout << "Enter the id you want to delete: ";
std::cin >> id;
deleteBasedOnID(head, tail, id);
std::cout << "New sorted list" << std::endl;
display();
return 0;
}

Answer 1

In your deleteBasedOnId-function, you change the value for the parameter head, which is a copy of the pointer to head you made in main. The original pointer in main keeps its value, which now points to deleted memory, hence the segfault. You can take a reference to the pointer to head as parameter to solve this problem:
void deleteBasedOnID(student*& head,student*& tail,int stu_ID)