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The QIntDict class is a template class that provides a dictionary based on long keys. More...
#include <qintdict.h>
Inherits QPtrCollection.
QIntDict is implemented as a template class. Define a template instance QIntDict<X> to create a dictionary that operates on pointers to X, or X*.
A dictionary is a collection of key-value pairs. The key is an long used for insertion, removal and lookup. The value is a pointer. Dictionaries provide very fast insertion and lookup.
The size() of the dictionary 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. Size is set in the constructor but may be changed with resize().
Items are inserted with insert(), and removed with remove(). All the items in a dictionary can be removed with clear(). The number of items in the dictionary is returned by count(). If the dictionary contains no items isEmpty() returns TRUE. You can change an item's value with replace(). Items are looked up with operator[](), or with find() which return a pointer to the value or 0 if the given key does not exist. You can take an item out of the dictionary with take().
Calling setAutoDelete(TRUE) for a dictionary tells it to delete items that are removed. The default behaviour is not to delete items when they are removed.
QIntDict is implemented 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 function. 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 QIntDict 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.
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.
The QIntDictIterator class can traverse the dictionary, but only in an arbitrary order. Multiple iterators may independently traverse the same dictionary.
When inserting an item into a dictionary, only the pointer is copied, not the item itself, i.e. a shallow copy is made. It is possible to make the dictionary copy all of the item's data (a deep copy) when an item is inserted. insert() calls the virtual function QPtrCollection::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 QPtrCollection::deleteItem() is called. QIntDict's default implementation is to delete the item if auto-deletion is enabled.
Example:
#include <qintdict.h> #include <stdio.h> int main() { QIntDict<char> dict; // maps long ==> char* dict.insert( 33, "France" ); dict.insert( 7, "Russia" ); dict.insert( 49, "Norway" ); dict.insert( 28, "Belgium" ); printf( "%s\n", dict[49] ); printf( "%s\n", dict[33] ); printf( "%s\n", dict[7] ); printf( "%s\n", dict[28] ); dict.remove( 28 ); if ( !dict[39] ) printf( "39 not defined\n" ); // Never existed if ( !dict[28] ) printf( "28 not defined\n" ); // Removed return 0; }
Program output:
Norway France Russia Belgium 39 not defined 28 not defined
The dictionary in our example maps long keys to char* items. QIntDict implements the [] operator to look up an item.
See also QIntDictIterator, QDict, QAsciiDict, QPtrDict and Collection Classes.
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.
Each item in dict is inserted into this dictionary. Only the pointers are copied (shallow copy).
All iterators that access this dictionary will be reset.
See also setAutoDelete().
Returns the setting of the auto-delete option. The default is FALSE.
See also setAutoDelete().
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 QPtrCollection.
See also isEmpty().
Reimplemented from QPtrCollection.
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[]().
Example: table/bigtable/main.cpp.
The key does not have to be unique. If multiple items are inserted with the same key, only the last item will be visible.
Null items are not allowed.
See also replace().
Example: scribble/scribble.cpp.
See also count().
This dictionary is first cleared and then each item in dict is inserted into this dictionary. Only the pointers are copied (shallow copy), unless newItem() has been reimplemented.
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().
The default implementation sets item to 0.
See also write().
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's traversing order.
See also take(), clear() and setAutoDelete().
Example: table/bigtable/main.cpp.
If the dictionary has key key, this key's item is replaced with item. If the dictionary doesn't contain key key, item is inserted into the dictionary using key key.
Null items are not allowed.
Equivalent to:
QIntDict<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 last inserted of these will be replaced.
See also insert().
Example: table/bigtable/main.cpp.
Sets the collection to auto-delete its contents if enable is TRUE and to never delete them if enable is FALSE.
If auto-deleting is turned on, all the items in a collection are deleted when the collection itself is deleted. This can be quite convenient if the collection has the only pointer to the items.
The default setting is FALSE, for safety. If you turn it on, be careful about copying the collection - you might find yourself with two collections deleting the same items.
See also autoDelete().
Examples: grapher/grapher.cpp, scribble/scribble.cpp and table/bigtable/main.cpp.
See also count().
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's traversing order.
See also remove(), clear() and setAutoDelete().
See also read().
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