Thread: hashing a string to an int question

Hi guys,

I am trying to make a hashing function that will accept a string and output an integer. On this forum I found this code (made by Salem) which adds up the ASCII values of the letters.

Code:

char string[] = "Bob Jones";

int hash ( const char *string ) {
  int result = 0;
  while ( *string ) result += *string++;
  return result;
}

It works fine for using character array stings, however, I would prefer to use a string declared as..

Code:

string name = "Bob Jones";

Is there anyway to accomplish the same thing using strings?

So the string is a class that has a member function named str?

Originally Posted by Mario F.

name.c_str() instead

Ah! Is the general structure of the string class posted anywhere? I would like to familiarize myself with it's member functions/data members (I'm still kind of new to this).

Sweet! Just what I needed. Thanks Mario F.!

Originally Posted by Prelude

>On this forum I found this code (made by Salem) which adds up the ASCII values of the letters.
I remember that. I also seem to remember that he mentioned how awful it is. Not only is the algorithm poor for hashing, it's also dangerous because it's so very easy to overflow an int. Here's a better one:

Code:

unsigned hash ( const char *key )
{
  unsigned h = 0;

  for ( int i = 0; key[i] != '\0'; i++ )
    h = 33 * h + key[i];

  return h;
}

>Is there anyway to accomplish the same thing using strings?

Code:

int h = hash ( name.c_str() );

Thanks Prelude,

I did modify the code from it's original form. I simply posted it like that because it was simpler. Thank you for the suggestions, they've given me some new ideas.