C++ error message

Question

I'm getting the error message segmentation fault for the following function. I was wondering if anyone could help me fix this problem

Polynomial Polynomial :: multiply(const Polynomial& p) const{
  //The functions returns the mathematical product of the host polynomial and p

  // new object created
  Polynomial multiply;
  // node that points to the beginning of the list
  Node *temporary = m_head;

  Node *copy = p.m_head;

  long num_coeff;

  unsigned int num_deg;

  while(temporary -> m_next != NULL){
    copy = p.m_head;
    while(copy -> m_next != NULL){
      Polynomial variable;
      num_coeff = temporary -> m_coefficient * copy -> m_coefficient;
      num_deg = temporary -> m_degree + copy -> m_degree;
      variable.insertMonomial(num_coeff, num_deg);
      multiply.add(variable);
      copy = copy -> m_next;
    }
    temporary = temporary -> m_next;
  }
  return multiply; 
}

where exactly is the segmentation fault occuring? Are you sure `m_head` is not null on entry to the function? how about `p.m_head`? — GreatAndPowerfulOz, Oct 29 '15 at 02:11
I'd just use a `std::vector` rather than a linked list. And if you feel that you absolutely must use a linked list, well there's `std::list` for you. Problem solved. — Cheers and hth. - Alf, Oct 29 '15 at 02:11
Thank you! I did initialize m_head to be null in the beginning. — John, Oct 29 '15 at 02:18

score 0 · Answer 1 · answered Oct 29 '15 at 02:26

I am willing to bet that you are running into segmentation fault because you don't have the right tests in the conditionals of the while statements.

You are using temporary -> m_next != NULL. What happens when temporary is NULL?

Instead of

while(temporary -> m_next != NULL){
   copy = p.m_head;
   while(copy -> m_next != NULL){

you should use

while(temporary != NULL){
   copy = p.m_head;
   while(copy != NULL){

C++ error message

1 Answers1