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qt3/doc/qintcache.doc

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/****************************************************************************
**
** QIntCache and QIntCacheIterator class documentation
**
** Copyright (C) 1992-2008 Trolltech ASA. All rights reserved.
**
** This file is part of the Qt GUI Toolkit.
**
** This file may be used under the terms of the GNU General
** Public License versions 2.0 or 3.0 as published by the Free
** Software Foundation and appearing in the files LICENSE.GPL2
** and LICENSE.GPL3 included in the packaging of this file.
** Alternatively you may (at your option) use any later version
** of the GNU General Public License if such license has been
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**
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** This file is provided "AS IS" with NO WARRANTY OF ANY KIND,
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** A PARTICULAR PURPOSE. Trolltech reserves all rights not granted
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**********************************************************************/
/*****************************************************************************
QIntCache documentation
*****************************************************************************/
/*!
\class QIntCache qintcache.h
\brief The QIntCache class is a template class that provides a cache based on long keys.
\ingroup collection
\ingroup tools
QIntCache is implemented as a template class. Define a template
instance QIntCache\<X\> to create a cache that operates on
pointers to X, or X*.
A cache is a least recently used (LRU) list of cache items,
accessed via \c long keys. 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) for a cache tells it to delete
items that are removed. The default is to not delete items when
they 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 dictionary and reimplement newItem() if you want deep
copies.
When removing a cache item, the item will be automatically
deleted if auto-deletion is enabled.
There is a QIntCacheIterator which may be used to traverse the
items in the cache in arbitrary order.
\sa QIntCacheIterator, QCache, QAsciiCache
*/
/*!
\fn QIntCache::QIntCache( const QIntCache<type> &c )
\internal
Do not use. A QCache cannot be copied. Calls tqFatal() in debug version.
*/
/*!
\fn QIntCache::QIntCache( int maxCost, int size )
Constructs a cache whose contents will never have a total cost
greater than \a maxCost and which is expected to contain less than
\a size items.
\a 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 is associated with a cost. When inserting a new
item, if the total cost of all items in the cache will exceed \a
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.
*/
/*!
\fn QIntCache::~QIntCache()
Removes all items from the cache and then destroys the int cache.
If auto-deletion is enabled the cache's items are deleted. All
iterators that access this cache will be reset.
*/
/*!
\fn QIntCache<type>& QIntCache::operator=( const QIntCache<type> &c )
\internal
Do not use. A QIntCache cannot be copied. Calls tqFatal() in debug version.
*/
/*!
\fn int QIntCache::maxCost() const
Returns the maximum allowed total cost of the cache.
\sa setMaxCost() totalCost()
*/
/*!
\fn int QIntCache::totalCost() const
Returns the total cost of the items in the cache. This is an
integer in the range 0 to maxCost().
\sa setMaxCost()
*/
/*!
\fn void QIntCache::setMaxCost( int m )
Sets the maximum allowed total cost of the cache to \a m. If the
current total cost is greater than \a m, some items are removed
immediately.
\sa maxCost() totalCost()
*/
/*!
\fn uint QIntCache::count() const
Returns the number of items in the cache.
\sa totalCost()
*/
/*!
\fn uint QIntCache::size() const
Returns the size of the hash array used to implement the cache.
This should be a bit larger than count() is likely to be.
*/
/*!
\fn bool QIntCache::isEmpty() const
Returns TRUE if the cache is empty; otherwise returns FALSE.
*/
/*!
\fn bool QIntCache::insert( long k, const type *d, int c, int p )
Inserts the item \a d into the cache with key \a k and assigns it
a cost of \a c (default 1). Returns TRUE if it succeeds; otherwise
returns FALSE.
The cache's size is limited, and if the total cost is too high,
QIntCache will remove old, least-used items until there is room
for this new item.
The parameter \a p is internal and should be left at the default
value (0).
\warning If this function returns FALSE (for example, the cost \c,
exceeds maxCost()), you must delete \a d yourself. Additionally,
be very careful about using \a d after calling this function. 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.
*/
/*!
\fn bool QIntCache::remove( long k )
Removes the item associated with \a 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 most recently is removed.
All iterators that refer to the removed item are set to point to
the next item in the cache's traversal order.
\sa take(), clear()
*/
/*!
\fn type * QIntCache::take( long k )
Takes the item associated with \a 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 most recently is taken.
All iterators that refer to the taken item are set to point to the
next item in the cache's traversal order.
\sa remove(), clear()
*/
/*!
\fn void QIntCache::clear()
Removes all items from the cache, and deletes them if
auto-deletion has been enabled.
All cache iterators that operate this on cache are reset.
\sa remove() take()
*/
/*!
\fn type * QIntCache::find( long k, bool ref ) const
Returns the item associated with \a k, or 0 if the key does not
exist in the cache. If \a 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 most recently is returned.
*/
/*!
\fn type * QIntCache::operator[]( long k ) const
Returns the item associated with \a k, or 0 if \a 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 most recently is returned.
This is the same as find( k, TRUE ).
\sa find()
*/
/*!
\fn void QIntCache::statistics() const
A debug-only utility function. Prints out cache usage, hit/miss,
and distribution information using tqDebug(). This function does
nothing in the release library.
*/
/*****************************************************************************
QIntCacheIterator documentation
*****************************************************************************/
/*!
\class QIntCacheIterator qcache.h
\brief The QIntCacheIterator class provides an iterator for QIntCache collections.
\ingroup collection
\ingroup tools
Note that the traversal order is arbitrary; you are not guaranteed
any particular order. If new objects are inserted into the cache
while the iterator is active, the iterator may or may not see
them.
Multiple iterators are completely independent, even when they
operate on the same QIntCache. QIntCache updates all iterators
that refer an item when that item is removed.
QIntCacheIterator provides an operator++(), and an operator+=() to
traverse the cache; current() and currentKey() to access the
current cache item and its key; atFirst() atLast(), which return
TRUE if the iterator points to the first/last item in the cache;
isEmpty(), which returns TRUE if the cache is empty; and count(),
which returns the number of items in the cache.
Note that atFirst() and atLast() refer to the iterator's arbitrary
ordering, not to the cache's internal least recently used list.
\sa QIntCache
*/
/*!
\fn QIntCacheIterator::QIntCacheIterator( const QIntCache<type> &cache )
Constructs an iterator for \a cache. The current iterator item is
set to point to the first item in the \a cache (or rather, the
first item is defined to be the item at which this constructor
sets the iterator to point).
*/
/*!
\fn QIntCacheIterator::QIntCacheIterator (const QIntCacheIterator<type> & ci)
Constructs an iterator for the same cache as \a ci. The new
iterator starts at the same item as ci.current(), but moves
independently from there on.
*/
/*!
\fn QIntCacheIterator<type>& QIntCacheIterator::operator=( const QIntCacheIterator<type> &ci )
Makes this an iterator for the same cache as \a ci. The new
iterator starts at the same item as ci.current(), but moves
independently thereafter.
*/
/*!
\fn uint QIntCacheIterator::count() const
Returns the number of items in the cache on which this iterator
operates.
\sa isEmpty()
*/
/*!
\fn bool QIntCacheIterator::isEmpty() const
Returns TRUE if the cache is empty; otherwise returns FALSE.
\sa count()
*/
/*!
\fn bool QIntCacheIterator::atFirst() const
Returns TRUE if the iterator points to the first item in the
cache; otherwise returns FALSE. Note that this refers to the
iterator's arbitrary ordering, not to the cache's internal least
recently used list.
\sa toFirst(), atLast()
*/
/*!
\fn bool QIntCacheIterator::atLast() const
Returns TRUE if the iterator points to the last item in the cache;
otherwise returns FALSE. Note that this refers to the iterator's
arbitrary ordering, not to the cache's internal least recently
used list.
\sa toLast(), atFirst()
*/
/*!
\fn type *QIntCacheIterator::toFirst()
Sets the iterator to point to the first item in the cache and
returns a pointer to the item.
Sets the iterator to 0, and returns 0, if the cache is empty.
\sa toLast() isEmpty()
*/
/*!
\fn type *QIntCacheIterator::toLast()
Sets the iterator to point to the last item in the cache and
returns a pointer to the item.
Sets the iterator to 0, and returns 0, if the cache is empty.
\sa toFirst() isEmpty()
*/
/*!
\fn QIntCacheIterator::operator type *() const
Cast operator. Returns a pointer to the current iterator item.
Same as current().
*/
/*!
\fn type *QIntCacheIterator::current() const
Returns a pointer to the current iterator item.
*/
/*!
\fn long QIntCacheIterator::currentKey() const
Returns the key for the current iterator item.
*/
/*!
\fn type *QIntCacheIterator::operator()()
Makes the succeeding item current and returns the original current
item.
If the current iterator item was the last item in the cache or if
it was 0, 0 is returned.
*/
/*!
\fn type *QIntCacheIterator::operator+=( uint jump )
Returns the item \a jump positions after the current item, or 0 if
it is beyond the last item. Makes this the current item.
*/
/*!
\fn type *QIntCacheIterator::operator-=( uint jump )
Returns the item \a jump positions before the current item, or 0
if it is beyond the first item. Makes this the current item.
*/
/*!
\fn type *QIntCacheIterator::operator++()
Prefix ++ makes the iterator point to the item just after
current(), and makes it the new current item for the iterator. If
current() was the last item, operator--() returns 0.
*/
/*!
\fn type *QIntCacheIterator::operator--()
Prefix -- makes the iterator point to the item just before
current(), and makes it the new current item for the iterator. If
current() was the first item, operator--() returns 0.
*/