C++ Error : Unhandled exception at 0x00934ABB (linked list, addressbook)

Question

I'm new to C++ and I have a project about creating this Address Book program and I'm having trouble with the code below. The code is supposed to create records.

cin >> ch;
switch(ch)
{
    case '1':
        system("cls");
        cout << "\n\nINSERT RECORD";
                        cout << "\n\nInput FIRST NAME: ";
                        cin.ignore();
                        getline(cin,firstname,'\n');
                        cout << "\n\nInput LAST NAME: ";
                        getline(cin,lastname,'\n');
                        cout << "\n\nInput PHONE NUMBER: ";
                        getline(cin,phonenumber,'\n');
                        cout << "\n\nInput DAY OF BIRTH: ";
                        getline(cin,dayofbirth,'\n');
                        cout << "\n\nInput MONTH OF BIRTH: ";
                        getline(cin,monthofbirth,'\n');
                        cout << "\n\nInput YEAR OF BIRTH: ";
                        getline(cin,yearofbirth,'\n');
                        cout << "\n\nInput AGE: ";
                        getline(cin,age,'\n');
                        cout << "\n\nInput STREET NAME (Address): ";
                        getline(cin,streetname,'\n');
                        cout << "\n\nInput CITY (Address): ";
                        getline(cin,city,'\n');
                        cout << "\n\nInput STATE (Address): ";
                        getline(cin,state,'\n');
                        cout << "\n\nInput ZIP CODE (Address): ";
                        getline(cin,zipcode,'\n');
                        cout << "\nRecord inserted!";
                    current = ad.AddNode(temp);
            ad.userPromptStatement();
    break;


    node* AddressBook::AddNode(nodePtr temp)
    { 
        string firstname;
        string lastname;
        string phonenumber;
        string dayofbirth;
        string monthofbirth;
        string yearofbirth;
        string age;
        string streetname;
        string city;
        string state;
        string zipcode;
        AddressBook ad;

           if(head != NULL)
            {
                current = head;
                while(current -> next != NULL)
                {
                    current = current -> next;
                }
                current = new node;
                current -> next -> firstname = temp -> firstname;
                current -> next -> lastname = temp -> lastname;
                current -> next -> phonenumber = temp -> phonenumber;
                current -> next -> dayofbirth = temp -> dayofbirth;
                current -> next -> monthofbirth = temp -> monthofbirth;
                current -> next -> yearofbirth = temp -> yearofbirth;
                current -> next -> age = temp -> age;
                current -> next -> streetname = temp -> streetname;
                current -> next -> city = temp -> city;
                current -> next -> state = temp -> state;
                current -> next -> zipcode = temp -> zipcode;
                current -> next = nullptr;
                return current;
                ad.userPromptStatement();
            }
           else
            {
                head = new node;
                head -> firstname = temp -> firstname;
                head -> lastname = temp -> lastname;
                head -> phonenumber = temp -> phonenumber;
                head -> dayofbirth = temp -> dayofbirth;
                head -> monthofbirth = temp -> monthofbirth;
                head -> yearofbirth = temp -> yearofbirth;
                head -> age = temp -> age;
                head -> streetname = temp -> streetname;
                head -> city = temp -> city;
                head -> state = temp -> state;
                head -> zipcode = temp -> zipcode;
                head -> next = nullptr;
                return current;
            }
    }

I keep getting an error in "xstring".

When I create 1 record, the error does not happen, but when I create the second one, I get this: "Unhandled exception at 0x00934ABB in dummy3.exe: 0xC0000005: Access violation reading location 0xCDCDCDE5."

bool _Grow(size_type _Newsize,
    bool _Trim = false)
    {   // ensure buffer is big enough, trim to size if _Trim is true
    if (max_size() < _Newsize)
        _Xlen();    // result too long
    if (this->_Myres < _Newsize) /*** <- next statement that will be executed points to this line ***/
        _Copy(_Newsize, this->_Mysize); // reallocate to grow
    else if (_Trim && _Newsize < this->_BUF_SIZE)
        _Tidy(true, // copy and deallocate if trimming to small string
            _Newsize < this->_Mysize ? _Newsize : this->_Mysize);
    else if (_Newsize == 0)
        _Eos(0);    // new size is zero, just null terminate
    return (0 < _Newsize);  // return true only if more work to do
    }

any ideas? I don't know anything about the "xstring" part..

You are accessing a null pointer. Probably helpful: ericlippert.com/2014/03/05/how-to-debug-small-programs/ — Samuel, Mar 07 '14 at 09:12
Your AddNode either (a) detects a NULL head, allocates a node, leaks its memory, then returns a mystery pointer, `current`, that was never set nor even declared in the function scope, or (b) detects a non-NULL head, walks to the end of the linked list, then promptly loses the pointer just-obtained to allocate a new node, dereferences its `next` incorrectly (repeatedly), returning a pointer to that new node but never adding it to the list. I.e this code has not yet begun to fight. — WhozCraig, Mar 07 '14 at 09:21
Is `temp` already dynamically allocated somewhere else, and all you want to do is link it to the tail end of the (potentially empty) linked list pointed to by `head` ? And where does `current` come from? This is clearly a function, yet neither `current` nor `head` seem to be declared or passed in. Post the **real** function, *with parameters*, **and** document any global/external variables. There are plenty of bugs in this code and fixing them is dependent on that info. — WhozCraig, Mar 07 '14 at 09:33
Don't start your variable/function/anything names from underscore : http://stackoverflow.com/questions/228783/what-are-the-rules-about-using-an-underscore-in-a-c-identifier — zoska, Mar 07 '14 at 09:49

Mike de Dood · Accepted Answer · 2014-03-07T09:44:13.017

1

Your problem lays here:

current = new node;
current -> next -> firstname = temp -> firstname;

You just created a new node (replacing current) and then you try to access its child (next) which is not initialized.

This should be better:

current -> next = new node;
current -> next -> firstname = temp -> firstname;
...
current -> next -> next = nullptr;
return current -> next;

Another hint: If tmp is dynamically created, then think about using it directly instead of copying its elements. Like this:

current -> next = tmp;

I don't know all of your code, so I cannot say if that works for you.

edited Mar 07 '14 at 09:44

answered Mar 07 '14 at 09:23

Mike de Dood

393
1
10

1

I'm fairly certain the `current = new node;` should be removed, and the rest remain as-is. look again. (the inappropriate return value not withstanding). – WhozCraig Mar 07 '14 at 09:26
Oh, yes. Now I get the error. I will update my answer. – Mike de Dood Mar 07 '14 at 09:27
1

yeah, *both* return value make no sense, nor is it clear whether the `temp` being passed in was itself dynamically allocated and should just be linked as `current->next`. (and the code as you have it now allocates a new node, then overwrites the content of the *existing* data of the `current` node, so it still isn't right). – WhozCraig Mar 07 '14 at 09:28
I added it to my answer, but to use it or not is his choice (maybe he has a good reason to copy it). – Mike de Dood Mar 07 '14 at 09:32

score 0 · Answer 2 · answered Mar 07 '14 at 09:18

0

The cause of that error propably is the trying to accessing null pointer.

You should create temp before use it. I couldnt see any pointer which name is temp. Please first create temp, and allocate it on memory with malloc or memset. Then you can pass the error.

answered Mar 07 '14 at 09:18

Cracker

500
7
21

1

This is C++, don't use "evil" malloc, use `new` and `delete`. – Mike de Dood Mar 07 '14 at 09:21
Yep new and delete is better malloc is another option in C thx for your opinion. – Cracker Mar 07 '14 at 09:22

C++ Error : Unhandled exception at 0x00934ABB (linked list, addressbook)

2 Answers2