Thread: Need some help with my Hash table

I'm working on an open chaining hash table. I've got the following code set up. My goal is to print the hash table in order (I know it's not ideal, but it's the assignment), but from a data file of 400 names, I'm only getting three names repeatedly. Could anyone let me know what I'm doing wrong?

Code:

#include <list>
#include <iostream>    
#include <fstream>        
#include <iomanip>
#include <string>


#include "sortedListADT.h"


using namespace std;


int BPHash(const string &str);




// This main program asks for the data file name then uses ONE of the 
// hash functions provided
int main(){
    string filename = ""; 
    string inputStr = ""; 
    int i;                
    ifstream inFile;     
    unsigned int hashVal; 
    sortedListADT<string> hashTab[211];  
    int numElements = 0;  


    
    cout << "Please enter the name of the data file to read: ";
    cin >> filename;


    //pass filename to inFile.open function
    inFile.open(filename);
    
    //if input file is not found, exit
    if(!inFile){
        cerr << "unable to open file. \n";
        exit(1);
    }
    
    //read the input file, count number of strings
    while(getline(inFile, inputStr)){
        //calculate the hash value of the input string, 
        //the result will be the index
        hashVal = BPHash(inputStr);
        //add input string to the hash table at the index
        hashTab[hashVal % 211].insertElement(inputStr);
        numElements++;
    }


    for(i = 0; i < numElements; i++){
        hashTab->printInOrder();
    }


    return 0;
}


// implementation of the BPHash function
int BPHash(const string &str){
    unsigned int hash = 0;
    for(std::size_t i = 0; i < str.length(); i++){
        hash = hash << 7 ^ str[i];
    }


    return hash;
}

If you plan to use hash tables, why not to use set<> or multiset<>?

Originally Posted by flp1969

If you plan to use hash tables, why not to use set<> or multiset<>?

I would like to, but my assignment specifies to use list, queue, deque.

Originally Posted by Salem

> hashTab->printInOrder();
This is like
hashTab[0].printInOrder();

Maybe you want your loop subscript in there.

Ah yeah, it might help if my debugging skills were up to par. From what my understanding is, the first line of my data file is hashed, and input into the table, and the loop repeats. If a collision occurs, the name is added to the linked list. This is why, when I print each element of the list, other names appear inside that element. Is this correct?

Originally Posted by Salem

Consider making the table size a constant.

You're absolutely right and I figured what I'm doing. I'm pretty dense, and sometimes things need to be bashed right into the center of my forehead. I think I'm good.