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The QPtrDict class is a template class that provides a dictionary based on void* keys. More...
#include <qptrdict.h>
Inherits QPtrCollection.
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> int 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]" ); 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" ); return 0; }
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 operator[] to look up 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. QPtrDict then 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> int main() { QPtrDict<char> dict; // maps char* ==> char* double *ptr = new double[28]; dict.insert( ptr, "first" ); dict.insert( ptr, "second" ); printf( "%s\n", dict[ptr] ); dict.remove( ptr ); printf( "%s\n", dict[ptr] ); return 0; }
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 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. QPtrDict's default implementation is to delete the item if auto-deletion is enabled.
See also QPtrDictIterator, QDict, QAsciiDict, QIntDict 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 are 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[]().
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().
See also count().
This dictionary is first cleared and then each item in dict is inserted into the 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 traversal order.
See also take(), clear() and setAutoDelete().
If the item does not already exist, item is 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 last inserted of these will be replaced.
See also insert().
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 traversal order.
See also remove(), clear() and setAutoDelete().
See also read().
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