Class Poco::LinearHashTable

File Information

Library: Foundation
Package: Hashing
Header: Poco/LinearHashTable.h

Description

This class implements a linear hash table.

In a linear hash table, the available address space grows or shrinks dynamically. A linear hash table thus supports any number of insertions or deletions without lookup or insertion performance deterioration.

Linear hashing was discovered by Witold Litwin in 1980 and described in the paper LINEAR HASHING: A NEW TOOL FOR FILE AND TABLE ADDRESSING.

For more information on linear hashing, see <http://en.wikipedia.org/wiki/Linear_hash>.

The LinearHashTable is not thread safe.

Value must support comparison for equality.

Find, insert and delete operations are basically O(1) with regard to the total number of elements in the table, and O(N) with regard to the number of elements in the bucket where the element is stored. On average, every bucket stores one element; the exact number depends on the quality of the hash function. In most cases, the maximum number of elements in a bucket should not exceed 3.

Member Summary

Member Functions: begin, bucketAddress, bucketAddressForHash, buckets, calcSize, clear, count, empty, end, erase, find, insert, merge, operator =, size, split, swap

Nested Classes

class ConstIterator

class Iterator

Types

Bucket

typedef std::vector < Value > Bucket;

BucketIterator

typedef typename Bucket::iterator BucketIterator;

BucketVec

typedef std::vector < Bucket > BucketVec;

BucketVecIterator

typedef typename BucketVec::iterator BucketVecIterator;

ConstPointer

typedef const Value * ConstPointer;

ConstReference

typedef const Value & ConstReference;

Hash

typedef HashFunc Hash;

Pointer

typedef Value * Pointer;

Reference

typedef Value & Reference;

ValueType

typedef Value ValueType;

Constructors

LinearHashTable

LinearHashTable(
std::size_t initialReserve = 64
);

Creates the LinearHashTable, using the given initialReserve.

LinearHashTable

LinearHashTable(
const LinearHashTable & table
);

Creates the LinearHashTable by copying another one.

Destructor

~LinearHashTable

~LinearHashTable();

Destroys the LinearHashTable.

Member Functions

begin

ConstIterator begin() const;

Returns an iterator pointing to the first entry, if one exists.

begin

Iterator begin();

Returns an iterator pointing to the first entry, if one exists.

buckets

std::size_t buckets() const;

Returns the number of allocated buckets.

clear

void clear();

Erases all elements.

count

std::size_t count(
const Value & value
) const;

Returns the number of elements with the given value, with is either 1 or 0.

empty

bool empty() const;

Returns true iff the table is empty.

end

ConstIterator end() const;

Returns an iterator pointing to the end of the table.

end

Iterator end();

Returns an iterator pointing to the end of the table.

erase

void erase(
Iterator it
);

Erases the element pointed to by it.

erase

void erase(
const Value & value
);

Erases the element with the given value, if it exists.

find

ConstIterator find(
const Value & value
) const;

Finds an entry in the table.

find

Iterator find(
const Value & value
);

Finds an entry in the table.

insert

std::pair < Iterator, bool > insert(
const Value & value
);

Inserts an element into the table.

If the element already exists in the table, a pair(iterator, false) with iterator pointing to the existing element is returned. Otherwise, the element is inserted an a pair(iterator, true) with iterator pointing to the new element is returned.