QAsciiCache(3qt)QAsciiCache(3qt)NAME
QAsciiCache - Template class that provides a cache based on char* keys
SYNOPSIS
#include <qasciicache.h>
Inherits QPtrCollection.
Public Members
QAsciiCache ( int maxCost = 100, int size = 17, bool caseSensitive =
TRUE, bool copyKeys = TRUE )
~QAsciiCache ()
int maxCost () const
int totalCost () const
void setMaxCost ( int m )
virtual uint count () const
uint size () const
bool isEmpty () const
virtual void clear ()
bool insert ( const char * k, const type * d, int c = 1, int p = 0 )
bool remove ( const char * k )
type * take ( const char * k )
type * find ( const char * k, bool ref = TRUE ) const
type * operator[] ( const char * k ) const
void statistics () const
DESCRIPTION
The QAsciiCache class is a template class that provides a cache based
on char* keys.
QAsciiCache is implemented as a template class. Define a template
instance QAsciiCache<X> to create a cache that operates on pointers to
X (X*).
A cache is a least recently used (LRU) list of cache items. The cache
items are accessed via char* keys. For Unicode keys use the QCache
template instead, which uses QString keys. A QCache has the same
performace as a QAsciiCache.
Each cache item has a cost. The sum of item costs, totalCost(), will
not exceed the maximum cache cost, maxCost(). If inserting a new item
would cause the total cost to exceed the maximum cost, the least
recently used items in the cache are removed.
Apart from insert(), by far the most important function is find()
(which also exists as operator[]()). This function looks up an item,
returns it, and by default marks it as being the most recently used
item.
There are also methods to remove() or take() an object from the cache.
Calling setAutoDelete(TRUE) tells the cache to delete items that are
removed. The default is to not delete items when then are removed
(i.e., remove() and take() are equivalent).
When inserting an item into the cache, only the pointer is copied, not
the item itself. This is called a shallow copy. It is possible to make
the cache 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 cache
and reimplement newItem() if you want deep copies.
When removing a cache item the virtual function
QPtrCollection::deleteItem() is called. Its default implementation in
QAsciiCache is to delete the item if auto-deletion is enabled.
There is a QAsciiCacheIterator which may be used to traverse the items
in the cache in arbitrary order.
See also QAsciiCacheIterator, QCache, QIntCache, Collection Classes,
and Non-GUI Classes.
MEMBER FUNCTION DOCUMENTATIONQAsciiCache::QAsciiCache ( int maxCost = 100, int size = 17, bool
caseSensitive = TRUE, bool copyKeys = TRUE )
Constructs a cache whose contents will never have a total cost greater
than maxCost and which is expected to contain less than size items.
size is actually the size of an internal hash array; it's usually best
to make it prime and at least 50% bigger than the largest expected
number of items in the cache.
Each inserted item has an associated cost. When inserting a new item,
if the total cost of all items in the cache will exceed maxCost, the
cache will start throwing out the older (least recently used) items
until there is enough room for the new item to be inserted.
If caseSensitive is TRUE (the default), the cache keys are case
sensitive; if it is FALSE, they are case-insensitive. Case-insensitive
comparison only affects the 26 letters in US-ASCII. If copyKeys is TRUE
(the default), QAsciiCache makes a copy of the cache keys, otherwise it
copies just the const char * pointer - slightly faster if you can
guarantee that the keys will never change, but very risky.
QAsciiCache::~QAsciiCache ()
Removes all items from the cache and destroys it. All iterators that
access this cache will be reset.
void QAsciiCache::clear () [virtual]
Removes all items from the cache, and deletes them if auto-deletion has
been enabled.
All cache iterators that operate on this cache are reset.
See also remove() and take().
Reimplemented from QPtrCollection.
uint QAsciiCache::count () const [virtual]
Returns the number of items in the cache.
See also totalCost() and size().
Reimplemented from QPtrCollection.
type * QAsciiCache::find ( const char * k, bool ref = TRUE ) const
Returns the item with key k, or 0 if the key does not exist in the
cache. If ref is TRUE (the default), the item is moved to the front of
the least recently used list.
If there are two or more items with equal keys, the one that was
inserted last is returned.
bool QAsciiCache::insert ( const char * k, const type * d, int c = 1, int p =
0 )
Inserts the item d into the cache using key k, and with an associated
cost of c. Returns TRUE if the item is successfully inserted. Returns
FALSE if the item is not inserted, for example, if the cost of the item
exceeds maxCost().
The cache's size is limited, and if the total cost is too high,
QAsciiCache will remove old, least recently used items until there is
room for this new item.
Items with duplicate keys can be inserted.
The parameter p is internal and should be left at the default value
(0).
Warning: If this function returns FALSE, you must delete d yourself.
Additionally, be very careful about using d after calling this
function, because any other insertions into the cache, from anywhere in
the application or within Qt itself, could cause the object to be
discarded from the cache and the pointer to become invalid.
bool QAsciiCache::isEmpty () const
Returns TRUE if the cache is empty; otherwise returns FALSE.
int QAsciiCache::maxCost () const
Returns the maximum allowed total cost of the cache.
See also setMaxCost() and totalCost().
type * QAsciiCache::operator[] ( const char * k ) const
Returns the item with key k, or 0 if k does not exist in the cache, and
moves the item to the front of the least recently used list.
If there are two or more items with equal keys, the one that was
inserted last is returned.
This is the same as find( k, TRUE ).
See also find().
bool QAsciiCache::remove ( const char * k )
Removes the item with key k and returns TRUE if the item was present in
the cache; otherwise returns FALSE.
The item is deleted if auto-deletion has been enabled, i.e., if you
have called setAutoDelete(TRUE).
If there are two or more items with equal keys, the one that was
inserted last is removed.
All iterators that refer to the removed item are set to point to the
next item in the cache's traversal order.
See also take() and clear().
void QAsciiCache::setMaxCost ( int m )
Sets the maximum allowed total cost of the cache to m. If the current
total cost is greater than m, some items are removed immediately.
See also maxCost() and totalCost().
uint QAsciiCache::size () const
Returns the size of the hash array used to implement the cache. This
should be a bit bigger than count() is likely to be.
void QAsciiCache::statistics () const
A debug-only utility function. Prints out cache usage, hit/miss, and
distribution information using qDebug(). This function does nothing in
the release library.
type * QAsciiCache::take ( const char * k )
Takes the item associated with k out of the cache without deleting it
and returns a pointer to the item taken out, or 0 if the key does not
exist in the cache.
If there are two or more items with equal keys, the one that was
inserted last is taken.
All iterators that refer to the taken item are set to point to the next
item in the cache's traversal order.
See also remove() and clear().
int QAsciiCache::totalCost () const
Returns the total cost of the items in the cache. This is an integer in
the range 0 to maxCost().
See also setMaxCost().
SEE ALSO
http://doc.trolltech.com/qasciicache.html
http://www.trolltech.com/faq/tech.html
COPYRIGHT
Copyright 1992-2007 Trolltech ASA, http://www.trolltech.com. See the
license file included in the distribution for a complete license
statement.
AUTHOR
Generated automatically from the source code.
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Trolltech AS 2 February 2007 QAsciiCache(3qt)