QPtrDict(3qt)QPtrDict(3qt)NAMEQPtrDict - Template class that provides a dictionary based
on
#include <qptrdict.h>
Inherits QGDict.
Public Members
QPtrDict ( int size=17 )
QPtrDict ( const QPtrDict<type> & dict )
~QPtrDict ()
QPtrDict<type>& operator= ( const QPtrDict<type> & dict )
virtual uint count () const
uint size () const
bool isEmpty () const
void insert ( void * key, const type * item )
void replace ( void * key, const type * item )
bool remove ( void * key )
type* take ( void * key )
type* find ( void * key ) const
type* operator[] ( void * key ) const
virtual void clear ()
void resize ( uint newsize )
void statistics () const
DESCRIPTION
The QPtrDict class is a template class that provides a
dictionary based on void* keys.
QPtrDict is implemented as a template class. Define a
template instance QPtrDict<X> to create a dictionary that
operates on pointers to X, or X*.
A dictionary is a collection that associates an item with
a key. The key is used for inserting and looking up an
item. QPtrDict has void* keys.
The dictionary has very fast insertion and lookup.
Example:
#include <qptrdict.h>
#include <stdio.h>
void main()
{
int *a = new int[12];
int *b = new int[10];
int *c = new int[18];
int *d = new int[13];
QPtrDict<char> dict; // maps void* -> char*
dict.insert( a, "a is int[12]" ); // describe pointers
dict.insert( b, "b is int[10]" );
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dict.insert( c, "c is int[18]" );
printf( "%s\n", dict[a] ); // print descriptions
printf( "%s\n", dict[b] );
printf( "%s\n", dict[c] );
if ( !dict[d] )
printf( "d not in dictionary\n" );
}
Program output:
a is int[12]
b is int[10]
c is int[18]
d not in dictionary
The dictionary in our example maps int* keys to char*
items. QPtrDict implements the [] operator to lookup an
item.
QPtrDict is implemented by QGDict as a hash array with a
fixed number of entries. Each array entry points to a
singly linked list of buckets, in which the dictionary
items are stored.
When an item is inserted with a key, the key is converted
(hashed) to an integer index into the hash array using the
mod operation. The item is inserted before the first
bucket in the list of buckets.
Looking up an item is normally very fast. The key is again
hashed to an array index. Then QPtrDict scans the list of
buckets and returns the item found or null if the item was
not found. You cannot insert null pointers into a
dictionary.
The size of the hash array is very important. In order to
get good performance, you should use a suitably large
prime number. Suitable means equal to or larger than the
maximum expected number of dictionary items.
Items with equal keys are allowed. When inserting two
items with the same key, only the last inserted item will
be visible (last in, first out) until it is removed.
Example:
#include <qptrdict.h>
#include <stdio.h>
void main()
{
QPtrDict<char> dict; // maps char* ==> char*
double *ptr = new double[28];
dict.insert( ptr, "first" );
dict.insert( ptr, "second" );
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printf( "%s\n", dict[ptr] );
dict.remove( ptr );
printf( "%s\n", dict[ptr] );
}
Program output:
second
first
The QPtrDictIterator class can traverse the dictionary
contents, but only in an arbitrary order. Multiple
iterators may independently traverse the same dictionary.
Calling setAutoDelete(TRUE) for a dictionary tells it to
delete items that are removed . The default is to not
delete items when they are removed.
When inserting an item into a dictionary, only the pointer
is copied, not the item itself. This is called a shallow
copy. It is possible to make the dictionary copy all of
the item's data (known as a deep copy) when an item is
inserted. insert() calls the virtual function
QCollection::newItem() for the item to be inserted.
Inherit a dictionary and reimplement it if you want deep
copies.
When removing a dictionary item, the virtual function
QCollection::deleteItem() is called. QPtrDict's default
implementation is to delete the item if auto-deletion is
enabled.
See also QPtrDictIterator, QDict, QAsciiDict, QIntDict and
Collection Classes
MEMBER FUNCTION DOCUMENTATIONQPtrDict::QPtrDict ( const QPtrDict<;type> & dict )
Constructs a copy of dict.
Each item in dict are inserted into this dictionary. Only
the pointers are copied (shallow copy).
QPtrDict::QPtrDict ( int size=17 )
Constructs a dictionary using an internal hash array with
the size size.
Setting size to a suitably large prime number (equal to or
greater than the expected number of entries) makes the
hash distribution better and hence the loopup faster.
QPtrDict::~QPtrDict ()
Removes all items from the dictionary and destroys it.
All iterators that access this dictionary will be reset.
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See also setAutoDelete().
void QPtrDict::clear () [virtual]
Removes all items from the dictionary.
The removed items are deleted if auto-deletion is enabled.
All dictionary iterators that access this dictionary will
be reset.
See also remove(), take() and setAutoDelete().
Reimplemented from QCollection.
uint QPtrDict::count () const [virtual]
Returns the number of items in the dictionary.
See also isEmpty().
Reimplemented from QCollection.
type * QPtrDict::find ( void * key ) const
Returns the item associated with key, or null if the key
does not exist in the dictionary.
This function uses an internal hashing algorithm to
optimize lookup.
If there are two or more items with equal keys, then the
last inserted of these will be found.
Equivalent to the [] operator.
See also operator[]().
void QPtrDict::insert ( void * key, const type * item )
Inserts the key with the item into the dictionary.
The key does not have to be a unique dictionary key. If
multiple items are inserted with the same key, only the
last item will be visible.
Null items are not allowed.
See also replace().
bool QPtrDict::isEmpty () const
Returns TRUE if the dictionary is empty, i.e. count() ==
0. Returns FALSE otherwise.
See also count().
QPtrDict<;type> & QPtrDict::operator= ( const QPtrDict<type> &
dict )
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Assigns dict to this dictionary and returns a reference to
this dictionary.
This dictionary is first cleared, then each item in dict
is inserted into this dictionary. Only the pointers are
copied (shallow copy), unless newItem() has been
reimplemented().
type * QPtrDict::operator[] ( void * key ) const
Returns the item associated with key, or null if the key
does not exist in the dictionary.
This function uses an internal hashing algorithm to
optimize lookup.
If there are two or more items with equal keys, then the
last inserted of these will be found.
Equivalent to the find() function.
See also find().
bool QPtrDict::remove ( void * key )
Removes the item associated with key from the dictionary.
Returns TRUE if successful, or FALSE if the key does not
exist in the dictionary.
If there are two or more items with equal keys, then the
last inserted of these will be removed.
The removed item is deleted if auto-deletion is enabled.
All dictionary iterators that refer to the removed item
will be set to point to the next item in the dictionary
traversing order.
See also take(), clear() and setAutoDelete().
void QPtrDict::replace ( void * key, const type * item )
Replaces an item which has a key equal to key with item.
If the item does not already exist, it will be inserted.
Null items are not allowed.
Equivalent to:
QPtrDict<char> dict;
...
if ( dict.find(key) )
dict.remove( key );
dict.insert( key, item );
If there are two or more items with equal keys, then the
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last inserted of these will be replaced.
See also insert().
void QPtrDict::resize ( uint newsize )
Changes the size of the hashtable the newsize. The
contents of the dictionary are preserved, but all
iterators on the dictionary become invalid.
uint QPtrDict::size () const
Returns the size of the internal hash array (as specified
in the constructor).
See also count().
void QPtrDict::statistics () const
Debugging-only function that prints out the dictionary
distribution using qDebug().
type * QPtrDict::take ( void * key )
Takes the item associated with key out of the dictionary
without deleting it (even if auto-deletion is enabled).
If there are two or more items with equal keys, then the
last inserted of these will be taken.
Returns a pointer to the item taken out, or null if the
key does not exist in the dictionary.
All dictionary iterators that refer to the taken item will
be set to point to the next item in the dictionary
traversing order.
See also remove(), clear() and setAutoDelete().
SEE ALSO
http://doc.trolltech.com/qptrdict.html
http://www.trolltech.com/faq/tech.html
COPYRIGHT
Copyright 1992-2001 Trolltech AS,
http://www.trolltech.com. See the license file included
in the distribution for a complete license statement.
AUTHOR
Generated automatically from the source code.
BUGS
If you find a bug in Qt, please report it as described in
http://doc.trolltech.com/bughowto.html. Good bug reports
make our job much simpler. Thank you.
In case of content or formattting problems with this
manual page, please report them to qt-bugs@trolltech.com.
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Please include the name of the manual page (qptrdict.3qt)
and the Qt version (2.3.1).
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