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**

** Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies).

** All rights reserved.

** Contact: Nokia Corporation (qt-info@nokia.com)

**

** This file is part of the documentation of the Qt Toolkit.

**

**

**

** If you have questions regarding the use of this file, please contact

** Nokia at qt-info@nokia.com.

** $QT_END_LICENSE$

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/*!

    \class Q3Cache

    \brief The Q3Cache class is a template class that provides a cache based on QString keys.

    \compat

    A cache is a least recently used (LRU) list of cache items. Each

    cache item has a key and a certain cost. The sum of item costs,

    totalCost(), never exceeds 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.

    Q3Cache is a template class. Q3Cache\<X\> defines a cache that

    operates on pointers to X, or X*.

    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 Q3PtrCollection::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

    Q3PtrCollection::deleteItem() is called. The default

    implementation deletes the item if auto-deletion is enabled, and

    does nothing otherwise.

    There is a Q3CacheIterator that can be used to traverse the items

    in the cache in arbitrary order.

    In Q3Cache, the cache items are accessed via QString keys, which

    are Unicode strings. If you want to use non-Unicode, plain 8-bit

    \c char* keys, use the Q3AsciiCache template. A Q3Cache has the

    same performance as a Q3AsciiCache.

    \sa Q3CacheIterator, Q3AsciiCache, Q3IntCache

*/

/*!

  \fn Q3Cache::Q3Cache( const Q3Cache<type> &c )

  \internal

  Do not use. A Q3Cache cannot be copied. Calls qFatal() in debug version.

*/

/*!

    \fn Q3Cache::Q3Cache( int maxCost, int size, bool caseSensitive )

    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 a prime number 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 \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.

    If \a caseSensitive is TRUE (the default), the cache keys are case

    sensitive; if it is FALSE, they are case-insensitive.

    Case-insensitive comparison considers all Unicode letters.

*/

/*!

    \fn Q3Cache::~Q3Cache()

    Removes all items from the cache and destroys it. All iterators

    that access this cache will be reset.

*/

/*!

  \fn Q3Cache<type>& Q3Cache::operator=( const Q3Cache<type> &c )

  \internal

  Do not use. A Q3Cache cannot be copied. Calls qFatal() in debug version.

*/

/*!

    \fn int Q3Cache::maxCost() const

    Returns the maximum allowed total cost of the cache.

    \sa setMaxCost() totalCost()

*/

/*!

    \fn int Q3Cache::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 Q3Cache::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 deleted

    immediately.

    \sa maxCost() totalCost()

*/

/*!

    \fn uint Q3Cache::count() const

    Returns the number of items in the cache.

    \sa totalCost()

*/

/*!

    \fn uint Q3Cache::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.

*/

/*!

    \fn bool Q3Cache::isEmpty() const

    Returns TRUE if the cache is empty; otherwise returns FALSE.

*/

/*!

    \fn bool Q3Cache::insert( const QString &k, const type *d, int c, int p )

    Inserts the item \a d into the cache with key \a k and associated

    cost, \a c. Returns TRUE if it is successfully inserted; otherwise

    returns FALSE.

    The cache's size is limited, and if the total cost is too high,

    Q3Cache will remove old, least recently 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 (which could happen, e.g.

    if the cost of this item alone exceeds maxCost()) you must delete

    \a d yourself. Additionally, be very careful about using \a 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.

*/

/*!

    \fn bool Q3Cache::remove( const QString &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 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.

    \sa take(), clear()

*/

/*!

    \fn type *Q3Cache::take( const QString &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 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.

    \sa remove(), clear()

*/

/*!

    \fn void Q3Cache::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 *Q3Cache::find( const QString &k, bool ref ) const

    Returns the item associated with key \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 last is returned.

*/

/*!

    \fn type *Q3Cache::operator[]( const QString &k ) const

    Returns the item associated with key \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 last is returned.

    This is the same as find( k, TRUE ).

    \sa find()

*/

/*!

    \fn void Q3Cache::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.

*/

/*****************************************************************************

  Q3CacheIterator documentation

 *****************************************************************************/

/*!

    \class Q3CacheIterator qcache.h

    \brief The Q3CacheIterator class provides an iterator for Q3Cache collections.

    \compat

    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 Q3Cache. Q3Cache updates all iterators that

    refer an item when that item is removed.

    Q3CacheIterator provides an operator++(), and an operator+=() to

    traverse the cache. The current() and currentKey() functions are

    used to access the current cache item and its key. The atFirst()

    and atLast() return TRUE if the iterator points to the first or

    last item in the cache respectively. The isEmpty() function

    returns TRUE if the cache is empty, and count() 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 Q3Cache

*/

/*!

    \fn Q3CacheIterator::Q3CacheIterator( const Q3Cache<type> &cache )

    Constructs an iterator for \a cache. The current iterator item is

    set to point to the first item in the \a cache.

*/

/*!

    \fn Q3CacheIterator::Q3CacheIterator (const Q3CacheIterator<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 Q3CacheIterator<type>& Q3CacheIterator::operator=( const Q3CacheIterator<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 Q3CacheIterator::count() const

    Returns the number of items in the cache on which this iterator

    operates.

    \sa isEmpty()

*/

/*!

    \fn bool Q3CacheIterator::isEmpty() const

    Returns TRUE if the cache is empty, i.e. count() == 0; otherwise

    it returns FALSE.

    \sa count()

*/

/*!

    \fn bool Q3CacheIterator::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 Q3CacheIterator::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 *Q3CacheIterator::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 *Q3CacheIterator::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 Q3CacheIterator::operator type *() const

    Cast operator. Returns a pointer to the current iterator item.

    Same as current().

*/

/*!

    \fn type *Q3CacheIterator::current() const

    Returns a pointer to the current iterator item.

*/

/*!

    \fn QString Q3CacheIterator::currentKey() const

    Returns the key for the current iterator item.

*/

/*!

    \fn type *Q3CacheIterator::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 *Q3CacheIterator::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 *Q3CacheIterator::operator-=( uint jump )

    Returns the item \a jump positions before the current item, or 0

    if it is before the first item. Makes this the current item.

*/

/*!

    \fn type *Q3CacheIterator::operator++()

    Prefix++ makes the iterator point to the item just after current()

    and makes that the new current item for the iterator. If current()

    was the last item, operator++() returns 0.

*/

/*!

    \fn type *Q3CacheIterator::operator--()

    Prefix-- makes the iterator point to the item just before

    current() and makes that the new current item for the iterator. If

    current() was the first item, operator--() returns 0.

*/