RWHashTable(3C++) RWHashTable(3C++)
NameRWHashTable - Rogue Wave library class
Synopsis
#include <rw/hashtab.h>
RWHashTable h ;
Description
This class is a simple hash table for objects inheriting from
RWCollectable. It uses chaining (as implemented by class
RWSlistCollectables) to resolve hash collisions. Duplicate objects are
allowed. An object stored by RWHashTable must inherit from the abstract
base class RWCollectable, with suitable definition for virtual functions
hash() and isEqual() (see class RWCollectable). To find an object that
matches a key, the key's virtual function hash() is first called to
determine in which bucket the object occurs. The bucket is then searched
linearly by calling the virtual function isEqual() for each candidate,
with the key as the argument. The first object to return TRUE is the
returned object. The initial number of buckets in the table is set by
the constructor. There is a default value. If the number of items in
the collection greatly exceeds the number of buckets then efficiency will
sag because each bucket must be searched linearly. The number of buckets
can be changed by calling member function resize(). This will require
that all objects be rehashed. The iterator for this class is
RWHashTableIterator.
Persistence
None
Example
#include <rw/hashtab.h>
#include <rw/colldate.h>
#include <rw/rstream.h>
main(){
RWHashTable table;
RWCollectableDate *july
= new RWCollectableDate(7, "July", 1990);
RWCollectableDate *may
= new RWCollectableDate (1, "May", 1977);
RWCollectableDate *feb
= new RWCollectableDate (22, "Feb", 1983);
RWCollectableDate *aug
= new RWCollectableDate (2, "Aug", 1966);
table.insert(july);
table.insert(may);
table.insert(feb);
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RWHashTable(3C++) RWHashTable(3C++)
table.insert(aug);
cout << "Table contains " << table.entries() << " entries.0;
RWCollectableDate key(22, "Feb", 1983);
cout << "It does ";
if (!table.contains(&key)) cout << "not ";
cout << "contain the key " << key << endl;
delete july;
delete may;
delete feb;
delete aug;
return 0;
}
Program output:
Table contains 4 entries.
Public Constructors
It does contain the key February 22, 1983
RWHashTable(size_t N = RWCollection::DEFAULT_CAPACITY);
Construct an empty hash table with N buckets.
RWHashTable(const RWHashTable& t);
Copy constructor. Create a new hash table as a shallow copy of the table
t. The new table will have the same number of buckets as the old table.
Hence, the members need not be and will not be rehashed.
Public Operators
void
operator=(const RWHashTable& t);
Assignment operator. Sets self as a shallow copy of t. Afterwards, the
two tables will have the same number of buckets. Hence, the members need
not be and will not be rehashed.
RWBoolean
operator==(const RWHashTable& t) const;
Returns TRUE if self and t have the same number of elements and if for
every key in self there is a corresponding key in t which isEqual.
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RWHashTable(3C++) RWHashTable(3C++)
RWBoolean
operator<=(const RWHashTable& t) const;
Returns TRUE if self is a subset of t, that is, every element of self
has a counterpart in t which isEqual. Note: If you inherit from
RWHashTable in the presence of the Standard C++ Library, we recommend
that you override this operator and explicitly forward the call.
Overload resolution in C++ will choose the Standard Library provided
global operators over inherited class members. These global definitions
are not appropriate for set-like partial orderings.
RWBoolean
operator!=(const RWHashTable&) const;
Returns the negation of operator==(), above.
Member Functions
virtual void
apply(RWapplyCollectable ap, void*);
Redefined from RWCollection. The function pointed to by ap will be
called for each member in the collection. Because of the nature of
hashing collections, this will not be done in any particular order. The
function should not do anything that could change the hash value or
equality properties of the objects.
virtual RWspace
binaryStoreSize() const;
Inherited from RWCollection.
virtual void
clear();
Redefined from RWCollection.
virtual void
clearAndDestroy();
Inherited from RWCollection.
virtual int
compareTo(const RWCollectable*) const;
Inherited from RWCollection.
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RWHashTable(3C++) RWHashTable(3C++)
virtual RWBoolean
contains(const RWCollectable*) const;
Inherited from RWCollection.
virtual size_t
entries() const;
Redefined from RWCollection.
virtual RWCollectable*
find(const RWCollectable*) const;
Redefined from RWCollection.
virtual unsigned
hash() const;
Inherited from RWCollection.
virtual RWCollectable*
insert(RWCollectable* a);
Redefined from RWCollection. Returns a if successful, nil otherwise.
virtual RWClassID
isA() const;
Redefined from RWCollection to return __RWHASHTABLE.
virtual RWBoolean
isEmpty() const;
Redefined from RWCollection.
virtual RWBoolean
isEqual(const RWCollectable*) const;
Redefined from RWCollection.
virtual RWCollectable*
newSpecies() const;
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RWHashTable(3C++) RWHashTable(3C++)
Redefined from RWCollection.
virtual size_t
occurrencesOf(const RWCollectable*) const;
Redefined from RWCollection.
virtual RWCollectable*
remove(const RWCollectable*);
Redefined from RWCollection.
virtual void
removeAndDestroy(const RWCollectable*);
Inherited from RWCollection.
virtual void
resize(size_t n = 0);
Resizes the internal hash table to have n buckets. This causes rehashing
all the members of the collection. If n is zero, then an appropriate
size will be picked automatically.
virtual void
restoreGuts(RWvistream&);
virtual void
restoreGuts(RWFile&);
virtual void
saveGuts(RWvostream&) const;
virtual void
saveGuts(RWFile&) const;
Inherited from class RWCollection.
RWStringID
stringID();
(acts virtual) Inherited from class RWCollectable.
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