C++ Hash Function
 Posted by Samath Last Updated: January 05, 2017   766

A hash function is any function that can be used to map data of arbitrary size to data of fixed size. The values returned by a hash function are called hash values, hash codes, digests, or simply hashes. This is a class example for writing a hash function and building a hash table. The width determines how many distinct values can the table holds and depth specify the length of the collision values.

```#include <iostream>
#include <stdio.h>
#include <string>
using namespace std;

class MyHash
{
private:
string ** table;
int * maxind;
long width;
long depth;

protected:
bool insert(long value,string s);
void printone(long v);

public:
MyHash(long N, long Depth);
long apply(string s);
void printall();
};

MyHash::MyHash(long N, long Depth)
{
this->width = N;
this->depth = Depth;
table = new string*[N];
maxind = new int[N];
for(long i =0; i < N ;i++)
{
table[i] = NULL;
}
}

long MyHash::apply(string s)
{
long accum = 0;
const int size = s.size();
const char * bytes = s.c_str();
for(int i =0; i < size; i++)
{
accum+= bytes[i];

}
accum  = (accum & (0x3FFFFFFF)) % width;
if(!insert(accum,s)) printf("Hash Table is full. Value is lost. \n");
return accum;
}

bool MyHash::insert(long v, string s)
{
if(table[v] == NULL)
{
table[v] = new string[depth];
maxind[v] = 0;
table[v][maxind[v]] = s;
maxind[v]++;
}
else
{
if(maxind[v] == depth)
{
return false;
}
table[v][maxind[v]] = s;
maxind[v]++;
}

return true;
}

void MyHash::printone(long v)
{
if(table[v] == NULL)
return;

for(int i =0; i < maxind[v]; i++)
{
cout << "(" << i <<") " <<table[v][i];
}

}

void MyHash::printall()
{
for(long i =0; i < width; i++)
{
cout << i << ": ";
printone(i);
printf("\n");
}
}

int main()
{
MyHash hinst(10,3);
hinst.apply("HelloWorld !");
hinst.apply("Hellold !") ;
hinst.apply("He= !") ;
hinst.apply("HelloWorld ! dfdfd");
hinst.apply("HelloWorld !");
hinst.apply("Abc") ;
hinst.apply("efg") ;

hinst.printall();

}```