Need help Debugging (ADT)

This is a discussion on Need help Debugging (ADT) within the C Programming forums, part of the General Programming Boards category; So how about you start checking your values before you start trying to use them? Code: void insertBeforeFirst(ListRef L, int ...

  1. #16
    ATH0 quzah's Avatar
    Join Date
    Oct 2001
    Posts
    14,826
    So how about you start checking your values before you start trying to use them?
    Code:
    void insertBeforeFirst(ListRef L, int data){
      NodeRef temp= newNode(data);
      if(L== NULL){
        printf("Queue Error: called insertBeforeFirst() on NULL ListRef\n");
        exit(1);
      }
      if(isEmpty(L)){ L->head= L->tail= temp; }
      else{
        temp->next = L->head;
        L->head->prev= temp;
        L->head= temp;
      }
      L->length++;
    }
    Check to see that ->head exits before you start trying to access its members. Never assume a pointer points somewhere valid. It's obvious it doesn't, since your debugger is telling you it doesn't.


    Quzah.
    Hope is the first step on the road to disappointment.

  2. #17
    and the Hat of Guessing tabstop's Avatar
    Join Date
    Nov 2007
    Posts
    14,185
    If this is a legitimate debugging session, then this would appear to be the first time you've inserted anything in the list -- yet the isEmpty test comes out false. Is this actually the first thing you are inserting in the list?

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