linked list of linked list

[mbw290]

I am trying to write a home made database, and my approach is to use a linked list of linked lists. The first linked list is the db and the underlying linked lists are the db tables. I am having trouble in my display method finding a table by name.

#include<iostream>
#include <stdio.h>
#include <vector>
using namespace std;
int counter=0;


template <class atype>
class Field
{
public:
    string name;
    atype val;
};


class dbTable
{
public:
    vector <int> intRow;
 
  	vector<Field<double> > doubleRow;

	vector<Field<string> > stringRow;
    
    string name;
};


//we need a link to point to the puppy and the next item
//something to hold the list and methods to add to the list and remove etc.
class Link
{
public:
    dbTable *table = new dbTable;
    Link *Next;
    Link *current;
    Field<int> *ifield;
    Field<string> *strfield;
    Field<double> *dfield;
};

class LinkedList
{
private:
    Link *First;
public:
    string name;
    LinkedList()
    {
        First = NULL;
    }
    

     vector<int> AddIntField(int i)
    {
        Link *newLink = new Link;
        dbTable *ntable = new dbTable;
        newLink->table=ntable;
	vector<int> m = newLink->table->intRow;
        vector<int>::iterator mit;
        mit=m.begin();
        m.insert(mit,i);
        newLink = newLink->Next;
        First= newLink;
        cout << "Int added";
        return m;
    }
    
    void AddStrField(Field<string> strfield)
    {
        Link *current;
        current = First;
        current->table->stringRow.push_back(strfield);
       // current = current->Next;
        cout << "String added";
    }
    
    void AddDoubleField(Field<double> dfield)
    {
        Link *current;
        current = First;
        current->table->doubleRow.push_back(dfield);
        //current = current->Next;
        cout << "Double added";
    }
    
    LinkedList addDbTable(string name)
    {
        Link *newLink = new Link;
        dbTable *nTable;
        newLink->table=nTable;
        newLink->Next=First;
        First=newLink;
        LinkedList LL;
        LL.name = name;
        counter++;
        return LL;
    }
    
    void AddTableEnd(int A,int B, string name)
    {
        
        
        Link *lastItem=new Link;
        Link *newNode=new Link;
        dbTable *nTable=new dbTable;
        lastItem=First;
       
        while (lastItem->Next != NULL)
        {
            lastItem=lastItem->Next;
        }
        lastItem->Next=newNode;
        newNode->table = nTable;
        newNode->table->name = name;
        newNode->Next=NULL;
    }
    
    void RemoveTable(string name)
    {
        string dName;
        while(First != NULL)
        {
            if(name.compare(name) == 0)
            {
                RemoveList(*First);
                cout << "Deleted " << endl;
                break;
            }
            First=First->Next;
        }
        
    }
    
    void RemoveList(Link L)
    {
        Link *current=new Link;
        Link *temp = new Link;
        dbTable *ntable = new dbTable;
        current->table=ntable;
        current=First;
        while (current != NULL)
        {
            temp=current->Next;
            delete current;
            current=temp;
        }
        delete current;
    }

      void DisplayTable(LinkedList L, string name)
    {
    Link *current = new Link;
    Link *temp = new Link;
    dbTable *nTable = new dbTable;
    current->table = current->table;
    cout << First->table->name;
	while (current != NULL)
	{
        string tname=current->table->name;
	cout << tname << "\n";
		if (name.compare(tname) == 0)
		{
		cout << "DISPLAY " << tname << "\n";
		break;
		}
	current=current->Next;
	}
    }
    

};

}

[AbstractionAnon]

You have some issues with the code you've posted.

Line 35: You can't do an assignment in a class declaration. You need to do this in Link's constructor.

Line 131: You're modifying the head of your list. This is a memory leak. You will lose the entries you pass.

You need to investigate inheritance. You're intermixing functions related to tables within your database along with columns within a table within the same class (Link). This is poor design.

You need to look at using std::list. There is no reason to write your own linked list class when one already exists.

I suggest you rethink your class structure. Consider a DataBase class which contains a std::list of dbTables. A dbTable should contain a std::list of columns.

Line 136: Why are you passing L in? You're not using it.
Line 140: What's the point of creating a new dbTable instance here?
Line 141: dbTable has no default constructor, so current->table points to an uninitialized dbTable entry.
Line 149: The only way to get here is if current == NULL, therefore, you're trying to delete a NULL pointer. Guaranteed to crash your program.

Line 152: Why are you passing in L? You never use it.
Line 154: Link has no default constructor, therefore all variables in current and temp are undefined.
Line 156: What's the point of creating a new dbTable here?
Line 157: What's the point of this statement? It does nothing.
Line 161,168: Members of current are initialized.

[mbw290]

Each table can have multiple data types. For example one table has a row that contains name(string) and ID number (int)