Array of linked lists in C++

Question

Some code for context:

class WordTable
{
    public:
        WordTable();
        ~WordTable();

        List* GetListByAlphaKey(char key);
        void AddListByKey(char key);
        bool ListExists(char key);
        bool WordExists(string word);
        void AddWord(string word);
        void IncrementWordOccurances(string word);
        void Print();
    private:     
        List *_listArray[33];
        int _GetIndexByKey(char key);
};


class TableBuilder
{
    public:
    TableBuilder();
    ~TableBuilder();
    void AnalyzeStream(fstream &inputStream);        
    void PrintResults();
    private:
        void _AnalyzeCursor(string data);
        bool _WordIsValid(string data);
        WordTable* _WordTable;        
};

struct Element {
public:
   string Word;
   int Occurances;
   Element* Next;
};


class List
{
    public:
        List();
        ~List();

        Element* AddElement(string word);       
        void DeleteElement(Element* element);       
        void Print();       
        void Delete();
        Element* First;
        bool WordExists(string word);
        void IncrementWordOccurances(string word);      
    private:
        void _PrintElementDetails(Element* element);
};

Requirements
I must analyze text, building array of linked lists (where array contains list for each letter; list contains every word found in text), then print out results.

Problem I can`t initialize array of lists in WordTable.cpp. I know that i've misunderstood something, but i got no ideas and time. Anyone?

P.s. Yeah, that's a homework. STOP giving me advices about best practices, please... :)

Looks like you need a space in between your star and your variable name: List *_listArray[33]; Is this a problem in the actual code? — AlbertoPL
– AlbertoPL, Commented May 10, 2009 at 22:51
No, you don't need a space. It doesn't affect the code's correctness at all. — C. K. Young
– C. K. Young, Commented May 10, 2009 at 22:53
This is homework according to a comment below. You need to label it as such. — jmucchiello
– jmucchiello, Commented May 11, 2009 at 12:59
I cannot see the reason you shouldn't follow good practices when doing homeworks... — Mehrdad Afshari
– Mehrdad Afshari, Commented May 12, 2009 at 10:28
Because we are not supposed to do your homework for you. Your homework is so you can learn. If we do it for you, you won't learn. That is how it influences answers. — jmucchiello
– jmucchiello, Commented May 12, 2009 at 13:03

sth · Accepted Answer · 2009-05-10 22:54:18Z

4

An initialization for _listArray would look like this:

WordTable::WordTable() {
  for (int i=0; i<33; i++)
    _listArray[i] = new List();
}

You don't really say what exactly the problem is so I'm not sure if this helps...

answered May 10, 2009 at 22:54

sth

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8 Comments

joce Over a year ago

Note: Use of magic numbers (33: what does it stand for??) is usually a bad idea.

Arnis Lapsa Over a year ago

Not always hard coding something is bad. 33 are letters of alphabet. I'm quite sure they won`t change next few days until my homework will be delivered. :)

Arnis Lapsa Over a year ago

sth, sorry, this one didn`t help. I tried it already. Throws segmentation error.

Stowelly Over a year ago

It is considered good practice to declare any constant numbers using const int letters = 33; or #define letters 33 just to improve readability and maintainability

James Hopkin Over a year ago

This answer is correct with the code you've given. Perhaps you need to check what List's constructor does, if this code crashes.

|

xian · Accepted Answer · 2009-05-10 22:54:34Z

3

It's because you're creating an array of pointers to lists. Either change it to List _listArray[33]; or initialize it like so:

for ( int i = 0; i < 33; ++i ) {
    _listArray[i] = new List();
}

// and to access methods
_listArray[i]->AddElement( "word" );

answered May 10, 2009 at 22:54

xian

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2 Comments

Arnis Lapsa Over a year ago

This is the problem, initialization in this way throws an error right after it tries to use indexer on _listArray.

xian Over a year ago

Could you post the definition of the List class, instead of just the declaration?

jmucchiello · Accepted Answer · 2009-05-11 00:35:42Z

3

It appears you are optimizing your linked lists by having an array of them, one for each first letter of the word. Don't do that.

Use std::map. Where the string is the word and the int is your count.

EDIT: If you ignore my advice... As has been pointed out your _listArray is actually an array of pointers, not an array of objects. I think you wanted an array of objects. Since the array is fixed length, and List has a default constructor, the simplest way to do that is to just say

List _listArray[33];

If you want dynamic allocation, you could do this instead:

List* _listArray;

And in the constructor:

_listArray = new List[33];

And in the destructor:

delete[] _listArray;

edited May 11, 2009 at 0:35

answered May 10, 2009 at 22:55

jmucchiello

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6 Comments

joce Over a year ago

While true, this does not adresses the poster's question re: how to initialize a linked list table.

jmucchiello Over a year ago

Arguably, one should not be making linked lists in C++. The STL implementation of List will work as well as or better than a hand spun linked list. Additionally the use for the linked list here is dubious as the poster intends to search it often and a linked list is not a proper data structure for frequent search. Simply answering the user's question is of less value than helping the user find a solution.

Arnis Lapsa Over a year ago

"It appears you are optimizing your linked lists by having an array of them, one for each first letter of the word. Don't do that." - This is exactly what i'm trying to do. Sadly that's one of the rules of my homework - to use self-made array of linked lists.

Arnis Lapsa Over a year ago

jmucchiello, i appreciate your good will, but i just need to understand it and get it done. no need for optimization tips&tricks.

jmucchiello Over a year ago

You should have said it was homework and you should have said you HAD to use an array of linked lists

|

Florin · Accepted Answer · 2009-05-11 14:10:28Z

0

Please don't reinvent the wheel (again) Use std::list it works correctly, is safer, is standard.

Second : you have design problems : element attribute in list is public, but you have a private method ???.

answered May 11, 2009 at 14:10

Florin

3 Comments

Arnis Lapsa Over a year ago

Reinventing the wheel is what he needs - that`s a homework. dooh.

Florin Over a year ago

And if is a homework, please when you describe the problem , describe exactly the requirements : for example : extract words from a text without using any c++ library.

Arnis Lapsa Over a year ago

Sorry for wasting your time... :)

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