Thread: Data Type Errors

Can anyone help with the below compiling errors please?

hash.cpp: In function 'int main()':
hash.cpp:51: error: invalid conversion from 'data*' to 'int'
hash.cpp:51: error: initializing argument 1 of 'data::data(int)'
linhash.h: In member function 'int linHashtable<dataType>::insert(const dataType&) [with dataType = data]':
hash.cpp:51: instantiated from here
linhash.h:60: error: passing 'const data' as 'this' argument of 'int data::getHashval(int)' discards qualifiers

Code:

#include <iostream>
#include "linhash.h"

/* Small program to explore using hash tables.

   1. The hash table takes up to 400 items
   2. The program generates 400 random six digit numbers.
   3. It uses a hashing routine to place them in the hash table.
   4. The program prints a report on the percantage of clashes that 
      occur for every 20 numbers placed in the table.
*/ 

using namespace std;

struct data
{
   int x;
   
   data() : x(-1) {
   }
   
   data(int n) : x(n) {
   }
   
   bool empty() {
      return (x < 0);
   }
   
   int getHashval(int range) {
      return (x % range);
   }
};

int main()
{
   const int SIZE = 400;
   int count, totalClashes=0;
   int clashes = 0, numClashes;
   data *dataPtr;
   
   // declare linera hash table
   linHashtable<data> hashTable(SIZE);

   // initialise the random number generator
   srand(1);

   // generate 400 six digit numbers and put in hash table
   for (count=1; count<=SIZE; count++) {
      // create 6 digit number and then insert in hash table
      dataPtr = new data(rand() % 1000000);    
      numClashes = hashTable.insert(dataPtr);
      
      // build up hashing data
      if (numClashes > 0) {
         totalClashes += numClashes;
         clashes++;
      }
         
      // print a report with each set of 20 numbers added to table
      if ((count+1) % 20 == 0)
      {
         cout << "% full = " << (count+1) * 100 / SIZE << "\n";
         cout << "% clashing = " << clashes * 100 / (count+1) << "\n";
         cout << "ave search time = " << (count+1 + totalClashes) / (count+1) << "\n\n";
      }
   }

   return 0;
}

>> linHashtable<data>

It looks like whatever linHashtable is, it is holding data objects, but you're trying to pass it a pointer. Perhaps instead of this:

Code:

dataPtr = new data(rand() % 1000000);

use this:

Code:

data dataObj(rand() % 1000000);

and just use dataObj instead of the pointer.

I got the code to work as below but I can't get it to work logically as it is supposed to. Does anyone know how to do it?

Code:

#include <iostream>
#include <algorithm>
#include "linhash.h"

/* Small program to explore using hash tables.

   1. The hash table takes up to 400 items
   2. The program generates 400 random six digit numbers.
   3. It uses a hashing routine to place them in the hash table.
   4. The program prints a report on the percantage of clashes that 
      occur for every 20 numbers placed in the table.
*/ 

using namespace std;

struct data
{
   int x;
   
   data() : x(-1) {
   }
   
   data(int n) : x(n) {
   }
   
   bool empty() {
      return (x < 0);
   }

   data(const data &other) : x(other.x)
   { cout << "hi";
   }
   
   int getHashval(int range) const {
      return (x % range);
   }
};

int main()
{
   const int SIZE = 400;
   int count, totalClashes=0;
   int clashes = 0, numClashes = 0;
   data *dataPtr;
   
   // declare linera hash table
   linHashtable<data> hashTable(SIZE);

   // initialise the random number generator
   srand(1);

   // generate 400 six digit numbers and put in hash table
   for (count=1; count<=SIZE;) {
      // create 6 digit number and then insert in hash table

      dataPtr = new data(rand() % 1000000);  
      numClashes = hashTable.insert(*dataPtr);
      
      // build up hashing data
      if (numClashes > 0) {
         totalClashes += numClashes;
         clashes++;
      }

      // print a report with each set of 20 numbers added to table
      if ((count) % 20 == 0)
      {
         cout << "% full = " << (count) * 100 / SIZE << "\n";
         cout << "% clashing = " << clashes * 100 / (count) << "\n";
         cout << "ave search time = " << (count + totalClashes) / (count) << "\n\n";
      }
 count++;
   }

   return 0;
}

Hi! Thx for that Mats. And how about my fault. I couldn't find the way to solve the problem above on my post. I did change and delete

Code:

numClashes = hashTable.insert(*dataPtr);

so it can compile but i can get the numClashes. This is an exercise for get knowing with hash.

In member function ‘int linHashtable<dataType>::insert(const dataType&) [with dataType = data]’:
hash.cpp:53: instantiated from here
linhash.h:60: error: passing ‘const data’ as ‘this’ argument of ‘int data::getHashval(int)’ discards qualifiers

the problems is on the line above.

Ah, i see. I keep focusing on the error and this "discard qualifier" a bit familiar but sometime blind.
Thanks alot. I need to practice more.