C++ :: Hash Function Implementation
Aug 26, 2013
I was trying to implement a hash function in c++. This is just for learning purposes and not for a class project or assignment question. I had some questions before I started programming it:
1) Is it meaningful to have a hash function which maps string to string, string to int, int to int, float to int?
2) Can we have a template implementation which does element to element hashing?
I looked at several sources for a clear understanding of concepts and implementation technique but could not find a good source for reading about hashing.
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Jun 3, 2013
How to construct a simple hash function ? When the program executes, it will ask for your name. Type your name and it will print out a "hash code" (a number) from that name.
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Apr 11, 2013
I am working on creating a program using HashTables. This is for homework. This is the first time I am using and creating HashTables, so forgive me in advance as to I don't know entirely what I am doing. The main problem I am having right now is incorporating my remove() function. I can get the code to compile, but when I run test the program out, it crashes. The error that I am receiving is list iterator is not decrementable Here is my hashtable class as well as my remove() function. Also need to incorporate a print method.
class HTable
{
public:
HTable(int size);
[Code]....
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Dec 15, 2014
Is it possible to create a hash table of function pointers so that functions can be referenced by their name (using a string?)
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Jul 20, 2013
I am having trouble with the implementation section of my code. The trouble I am having is with the """"string Name::RevereUsingString()""" function/method. I keep getting an error saying that """"control reaches end of non-void function"""". The two void function below the ""string Name::RevereUsingString()"" fuction/method are ok and ready to be worked on.
How to implement the ""string Name::RevereUsingString()"" correctly in the implementation section?
#include <iostream>
#include <string>
using namespace std;
//-------------Class Section------------------------------------
class Name {
[Code] .....
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May 30, 2013
I got a code of a BST and i need to create a function that will return the value of the parent that it's son/sons sum to the biggest sum - BST and not AVL.
I assume that the shortest code will be recursive but i didn't manage to get it right - i'll send the code without my function because it's wrong - l
#include <vector>
#include <iostream>
using namespace std;
//-----------------------------------------------------------------
// class Node
// a single Node from a binary tree
//-----------------------------------------------------------------
template <class T> class Node
[Code] ....
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Apr 25, 2013
I am doing fixed point implementation in c++ which is done by the following code
#ifndef __fixed_point_header_h__
#define __fixed_point_header_h__
#include <boost/assert.hpp>
#include <boost/static_assert.hpp>
#include <boost/operators.hpp>
#include <limits>
[Code] ....
I am getting the error ambiguous overload for âoperator<â in âbeta < ((-5.0e-1) * pi)â
I know the problem the static member function cannot access the members and objects of structs. am i right?
and how to solve this problem, do i need to implement the cossin_cordic function as a non member function.
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Apr 18, 2013
I have a problem with this function that adds a new value to the hash table or updates its data if the value already exists:
Code:
int tab_add(tab_disp *td, const object *value) the function should return:
TABDISP_OK if the value is correctly added, or TABDISP_ERROR if memory error, or TABDISP_INVALID if pointer td = NULL
The type of structure I am using is the following:
Code:
typedef struct {
char key[25];
char value[100];
} object;
[code]....
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Jul 29, 2013
Code: I have these two columns.
ID Group
0 2
1 2
2 3
3 4
4 4
5 4
6 4
7 4 Code: I want to store ID values on the bases of same Group, like we do in Hash table (key, value) .
Group ID
2 0,1
3 2
4 3,4,5,6,7
so when i said key 2 it will give me 0,1. how can i do it. As first i thought that i can use array of array but then how i can store the value of key. Now I am thinking of hash but i don't know how I will store and retrieve these values.
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Jun 3, 2013
For my homework I need to create a hash table with a size of 7. I also need to create a queue that holds 3 names maximum for each table position
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Feb 24, 2013
I am having problems with this function:
bool HashTable::insert(char const * const key, const Player& aPlayer) {
//calculate the insertion position (the index of the array)
size_t index = calculateIndex(key);
for(int i=0; i < capacity; i++) {
[Code] ....
The inserting part works just fine, but the checking for duplicates where I compare the two values is crashing my program.
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Jul 28, 2012
I have a doubt in the PJW algorithm of the Hash Table.
What is the logic in shifting the bytes by this specified number as specified in the pjw algorithm.
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May 15, 2014
I want a speed of O(1) in search, insertion and deletion.
is std::map<> the way to go?
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May 3, 2013
The point of this code is to get 15 names and then hash them. After one name is entered I get a segmentation Fault and the program crashes.
Code:
//driver file
#include <iostream>
#include <vector>
#include <string>
using namespace std;
[Code] ....
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Feb 25, 2013
I'm trying to retrieve the Player object from my hash table so I can edit the content of that object. Here is what I have.
Player* HashTable::retrieve(char * key, Player& aPlayer) {
//calculate the retrieval position (the index of the array)
size_t index = calculateIndex(key);
//search for the data in the chain (linked list)
node * curr = table[index];
char id[100];
[Code] .....
Here I'm calling the retrieve and I need to return a pointer of that object.
Player* PlayerDB::FetchPlayer(char* name) {
Player* info = new Player();
out << "Fetching player " << """ << name << "" -- ";
if(h.retrieve(name, *info)) {
out << "Success!" << endl;
[Code] .....
And here is my call in main.
Player* outPlayer = NULL;
outPlayer = pdb.FetchPlayer("Sappho");
if (outPlayer != NULL) {
outPlayer->LevelUp();
}
I'm just trying to change the actual level of the player using the LevelUp function, but right now it is not making that change. I've been told I need to return a reference of the object in my retrieve function, but I thought that was what I was doing already.
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Apr 25, 2013
I am getting a strange runtime error when trying to run my hash table program. I have it separated in 3 separate files. I believe I have narrowed down where the error is occurring. It is either happening in insert(const &string s) or in the implementation of vector<list<string>> ht. I would appreciate some input. This is the implementation of insert():
void HTable::insert(const string &s) {
int h = hash(s);
cout<<h<<endl;
list<string> &tempList = ht[h];
[Code] .....
And it is giving me some sort of compilation error saying I cannot convert a type string to type list.
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Nov 28, 2014
my insert() function
template <class T>
class Node
{
public:
[Code]....
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May 22, 2013
I am trying to generate a sha256 hash with std string, but i can't get this incomplete code puzzle to work [URL] .....
void main() {
string pbData1 = "HELLO";
BYTE* pbOutputBuffer;
CryptoPP::SHA256().CalculateDigest(pbOutputBuffer, (byte*)pbData1.c_str(), pbData1.size());
cout << pbOutputBuffer;
}
my problem is converting 'const char *' to 'const byte *' ..etc
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Apr 21, 2013
Here is my code so far:
Code:
//LINEAR CHAINING OR SEPERATE CHAINING...
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#define MAX_USERNAME_LEN 15
#define MAX_PASSWORD_LEN 20
[Code] ....
When I compile I get this error:
Code:
simpleauth.c: In function ‘initialize_table’:
simpleauth.c:179:30: error: incompatible types when assigning to type ‘DBEntry’ from type ‘void *’
I am sure its a simple error but I cannot seem to figure out how to set all the entries in the database to NULL. My plan is this:
1. Set all entries to NULL.
2. Check if entry is empty, if empty insert into hash-location, if not increment until empty...
Part 2 seems easy to me, but I cannot set them to empty....
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Nov 22, 2014
I have a large hash table, where each index has a container that has a doubly linked list. Things work up until releasing the memory. Each record is created with malloc, and each record->data is also created with malloc and the associated string is copied in using strcpy(). The table itself is released in another part of the program and doesn't produce and error.
/**
* valgrind --track-origins=yes
*/
==16898== Conditional jump or move depends on uninitialised value(s)
==16898== at 0x8049685: shFree (SpellHash.c:110)
==16898== by 0x8049352: unload (dictionary.c:115)
==16898== by 0x8048E64: main (speller.c:158)
==16898== Uninitialised value was created by a heap allocation
[Code] .....
How to interpret valgrind. Error resolved on a small problem. Now running into issues on large (>10000 words to check) problems. It appears the virtual machine just can't keep up for some reason. Running the code on my local computer produces no errors, memory usage is minuscule, and profile tools don't report any issues.
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Feb 28, 2013
I have following method to calculate a 16bit hash on a per definition unique string:
uint16_t IReferenceHolder::getHash(const std::string &ref) {
return std::inner_product(ref.begin(), ref.end(), ref.begin(), (uint16_t)0) % 65437;
}
Actually it calculates an inner product on each character adding it to the last result (see [URL] .....).
65437 is the nearest prime to 2^16. In fact I never need the full range of 16 bit, therefore 65437 different hashes are enough.
Empirically it seems - on unique strings - to be collision free. The strings have an maximum size of 255.
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May 16, 2013
My program had a requirement to ignore an input beginning with a # sign. The input is entered by user from keyboard. I wanted to know how to use cin.ignore to achieve this.
#include <iostream>
#include <algorithm>
#include <string>
#include <iomanip>
#include <limits>
#include <stdio.h>
using namespace std;
[Code] ....
The output:
Enter the string
# Comment
This is the # comment string.
Answer:
This is the string.
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Nov 5, 2013
I have an abstract based class and three derived classes. I also have a templated hash table class(using chaining as my collision resolution method, an array of stl lists), and a class to parse commands from a file, this also holds the instantiation of the hash table. My question is that since my command parsing class's constructor instantiates the hash table in the main driver(unable to modify) how can I make this dynamically allocated using data from the file?
template<class T>
class hashTable{
public:
hashTable(int size);
~hashTable();
[Code] .....
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Jul 24, 2014
I have this assignment where I have to create a map based hash table for a sparse matrix. The professor has provided some code and I'm supposed to fill in parts of it to make it work.
He has given us a class sparseMatrix which we need to provide a hash function for. This hash function is to be defined in a Class TupleHash which is inside sparseMatrix. I think I got that part down. What is really confusing me is what he has done with some typedefs.
For one of them I had to declare an unorderd_map that maps a struct Tuple on to the class template argument Object. I did that like so:
typedef unordered_map<Object,Tuple,TupleHash> HashTable;
The next typedef was given to me like so:
typedef typename HashTable::value_type valueType;
This is giving me a world of unintelligible error messages. This is how it starts.
In instantiation of 'struct std::__detail::__is_noexcept_hash<int, sparseMatrix<int>::TupleHash>':|
recursively required from 'struct std::__and_<std::is_default_constructible<sparseMatrix<int>::TupleHash>, std::is_copy_assignable<sparseMatrix<int>::TupleHash>, std::__detail::__is_noexcept_hash<int, sparseMatrix<int>::TupleHash> >'|
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Apr 10, 2013
I'm trying to write a little C++ wrapper around the PolarSLL SHA-512 / 384 implementation, the source code of which you can view here: [URL] .....
The problem I'm having is that the length of the digest is not always 64 bytes (for sha512) or 49 bytes (for sha384) as it's supposed to be, it often is, but not always.
I have pretty much used the code as it is on PolarSSL's website, except for wrapping it in an "impl" namespace. I also ran the self_tests, which all passed.
Here's the code I'm using to wrap the PolarSSL implementation:
namespace {
void sha4(const std::string& input, const sha_t& type, std::string& result) {
bool is_384 = (type == sha_t::SHA_384);
const unsigned char* in = reinterpret_cast<const unsigned char*>(input.c_str());
[Code] ....
When I do a strchr() for '' on the original (non-hex) values, the pointer position returned is the same as the checksums length, so I'm wondering if perhaps the sha4 implementation would shift bits around and one of them happens to become a '', null terminating the hash early?
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Nov 13, 2013
How difficult would it be to program a hash-map system where each "key" can have multiple values under indexes?
For example: "Word" -> 45(index 0) , 67(index 1) , 12(index 2). What could I start with to program this or where could I find a pre-made system that does this?
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