iflHashTable(3) Image Format Library C++ Reference Manual iflHashTable(3)NAME
iflHashTable, iflHashElem - base classes from which hash table
implementations may be derived
INHERITS FROM
This is a base class.
HEADER FILE
#include <ifl/iflHashTable.h>
CLASS DESCRIPTION
This class implements an abstract hash-based lookup table. To create a
hash table, a derived class must be defined that specifies the pure
virtual match() method. In addition, a hash function must be defined and
used to fill in the hashIndex field of any hash table elements (derived
from iflHashElem) that are to be inserted into the table. The match()
method is then used to compare elements when a collision occurs on the
hashIndex field.
The iflHashElem class is defined as:
struct iflHashElem {
unsigned int hashIndex;
};
It is used as a base from which to derive classes of elements to be
inserted into a hash table derived from iflHashTable. The constructor of
the derived class should fill in the hashIndex field with an appropriate
unsigned integer value for the hash index. The hash function used to map
a hash element to its hash index must be carefully chosed to minimize
collisions (different elements mapping to the same index) to get the best
performance from the hash table.
CLASS MEMBER FUNCTION SUMMARY
Constructor
iflHashTable(int maxEntries=0)
Manipulating
void clear()
int insert(iflHashElem* elem)
int remove(iflHashElem* elem)
Query
iflHashElem* find(unsigned int index, const void* key)
iflHashElem* next(int& index)
float getFullFraction() const
void setFullFraction(const float frac)
Page 1
iflHashTable(3) Image Format Library C++ Reference Manual iflHashTable(3)
Key matching
virtual int match(const void* key, protected
const iflHashElem* elem) = 0
Performance Statistics
int lookCount;
int totalLook;
int maxLook;
void clearStats()FUNCTION DESCRIPTIONSiflHashTable()
iflHashTable(int maxEntries=0)
Creates an empty iflHashTable, with initial size large enough to
hold maxEntries; the default value of zero will create a table with
131 slots. By default the hash table will automatically grow when
it gets more than half full. See setFullFraction() for more
details.
clear()
void clear()
Removes all elements currently in the hash table.
find()
iflHashElem* find(unsigned int index, const void* key)
Finds the element with hash index, index, and key value, key.
getFullFraction()
float getFullFraction() const
Returns the current fraction of the table, which when filled will
cause the hash table to be expanded. The default value is .5 (50%).
insert()
Page 2
iflHashTable(3) Image Format Library C++ Reference Manual iflHashTable(3)
void insert(iflHashElem* elem)
Inserts the hash element, elem, into the hash table. The hashIndex
field must already be filled in.
match()
virtual int match(const void* key, protected
const iflHashElem* elem) = 0
This function is used to compare an element key, key, with the key
of another element, elem. This function must be defined in any
class derived from iflHashTable.
next()
iflHashElem* next(int& index)
This function is used to iterate through the filled entries of a
hash table. To start iterating, index should be initiliazed to
zero. The index should not be altered on subsequent calls, as
iflHashTable uses it to keep track of where it is in the table. The
returned value is a pointer to the next hash element in the table,
or NULL, when there are no more entries left to iterate on in the
table.
remove()
void remove(iflHashElem* elem)
This function is used to remove the hash table element, elem, from
the table.
setFullFraction()
void setFullFraction(const float frac)
Sets the current fraction of the table, which when filled will cause
the hash table to be expanded. The default value is .5 (50%). If
frac is 1, the hash table will not grow, and insert() will fail when
the table is full.
clearStats()
void clearStats()
Page 3
iflHashTable(3) Image Format Library C++ Reference Manual iflHashTable(3)
Resets the lookCount, totalLook, and maxLook member variables to
zero. lookCount holds a running total of the number of lookups
(calls to find() or locate()). totalLook holds the number of hashes
and rehashes accumulated over all lookups. maxLook holds the
maximum number of rehashes ever required by a single lookup.
SEE ALSO
iflDictionary
Page 4
