Question

I am trying to convert a string into a unsigned char *. And i’ve been running in circles. My program prompts the user for a lastname which i take in as a string. I am then hashing the string into an integer using djb2. which takes an unsigned char * as a parameter. The goal of my program is to create a hash table using chaining to handle collisons.

unsigned long djb2(unsigned char *str)
{
    unsigned long hash = 5381;
    int c;

    while (c = *str++)
        hash = ((hash << 5) + hash) + c; /* hash * 33 + c */

    return hash;
}

my code is as follows atm.

void insert(LinkedList<Person>* HashList1[], LinkedList<Person>* HashList2[], int listSize)
{
    char * cstr;
    string str;
    cin >> str;
    cstr = new char [str.size()+1];
    strcpy (cstr, str.c_str());
    int hashBucket1 = djb2(cstr) % listSize;
}

Im getting an error with the above telling me that “Argument of type “char *” is incompatible with parameter of type “unsigned char *” . Any help is greatly appreciated

Answer 1

When you have typing issues like this, it’s a good indication that you are not using the language in the best way. Going back and forth between strings and char*s in C++ is a bad code smell.

Modify dbjc to use a string:

unsigned long djb2(const string& str)
{
    unsigned long hash = 5381;

    for(string::iterator it=str.begin();it!=str.end();it++) 
        hash = ((hash << 5) + hash) + *it; /* hash * 33 + character */

    return hash;
}

This will greatly simplify your insert:

void insert(LinkedList<Person>* HashList1[], LinkedList<Person>* HashList2[], int listSize){
    string str;
    cin >> str;
    int hashBucket1;
    hashBucket1 = djb2(str) % listSize;
}