Search Function Using Derived Classes in a Hash Table - c++

Question

I am having a bit of an issue with my derived classes and how they utilize the search function that they inherit from their parent class.
Here is my .h file
#include <iostream>
#include <string>
#include <cstdlib>
using namespace std;
#define TABLESIZE 13
#ifndef HASH_H
#define HASH_H
namespace HTGroup
{
template<class T>
class HashTable
{
protected:
struct item {
T x;
item* next;
};
item* HT[TABLESIZE];
virtual int hash(T key) = 0;
virtual int collision(T key, int &value) = 0;
public:
HashTable();
virtual void printGrid();
void insert(T key);
void remove(T key);
void search(T key);
int indexItems(int index);
};
template<class T>
class DHT1 : public HashTable<T>
{
protected:
int hash(T key);
int collision(T key, int &value);
struct item {
T x;
item* next;
};
item* HT[TABLESIZE];
public:
DHT1();
void printGrid();
};
template<class T>
class DHT2 : public HashTable<T>
{
protected:
int hash(T key);
int collision(T key, int &value);
struct item {
T x;
item* next;
};
item* HT[TABLESIZE];
public:
DHT2();
void printGrid();
};
}
#endif
Here is what I have implemented for the search function:
template<class T>
void HashTable<T>::search(T key)
{
int index = hash(key);
bool foundKey = false;
string item;
item* temp = HT[index];
while(temp != NULL)
{
if(temp->x == key)
{
foundKey = true;
item = temp->x;
}
temp = temp->next;
}
if(foundKey == true)
{
cout << "Item was found." << endl;
}
else
{
cout << "Item was not found." << endl;
}
}
And this is how I am calling the function in my main:
hashy1.search(item);
I am getting an error from the compiler with this line from my search implementation:
item* temp = HT[index];
Giving me this error:
[Error] 'temp' was not declared in this scope
From my understanding whenever an object of a derived class is calling the search function it is getting confused with whether or not the pointer created is of the parent class or the derived class.
The weird thing though is that it has let me create other pointers in my remove function without any issues and it works fine:
template<class T>
void HashTable<T>::remove(T key)
{
int index = hash(key);
item* delPtr; //Where I am allowed to create pointers with
item* P1; //no issues
item* P2;
if(HT[index]->x == "")
{
cout << key << " was not found in the hash table" << endl;
}
else if ( HT[index]->x == key && HT[index]->next == NULL)
{
HT[index]->x = "";
cout << key << " was removed from the hash table" << endl;
}
else if(HT[index]->x == key)
{
delPtr = HT[index];
HT[index] = HT[index]->next;
delete delPtr;
cout << key << " was removed from the hash table" << endl;
}
else
{
P1 = HT[index]->next;
P2 = HT[index];
while(P1 != NULL && P1->x != key)
{
P2 = P1;
P1 = P1->next;
}
if(P1 == NULL)
{
cout << key << " was not found in the hash table" << endl;
}
else
{
delPtr = P1;
P1 = P1->next;
P2->next = P1;
delete delPtr;
cout << key << " was removed from the hash table" << endl;
}
}
}
I've tried creating the pointer in the .h file like this:
template<class T>
class DHT1 : public HashTable<T>
{
protected:
int hash(T key);
int collision(T key, int &value);
struct item {
T x;
item* next;
item* temp; // Added declaration
};
item* HT[TABLESIZE];
public:
DHT1();
void printGrid();
};
But that still gives me declaration issues
Are there different methods I should be using when implementing my search function such as any extra parameters in the function call? Or maybe I am just not getting the logic down right?
Thank you for any responses!

Answer 1

You declared item as a std::string, and then you use item in the same scope as a type.
string item; // <-- declaring as string
item* temp = HT[index]; // <-- Compiler doesn't know what to do with this line except to give an error.
The simplest solution is to name your std::string variable something else other than item.